by Lawrence Elmes
Note: This paper was presented at the USAID/OAS PGDM building inspector training workshop, held in Antigua in January 2001
Report | Figures 1-3 | Pictures 1 - 9 | Pictures 10 - 20 | Pictures 21 - 29 | Pictures 30 - 39
The construction industry in St Kitts and Nevis has always been a very vibrant one and is currently a major contributor to economic activity in the Federation.
The styles of the early houses of the common folk of the islands was simple and direct and basic. It reflected the low economic status of the people. Over the years, given improved economic conditions, the houses have become larger and more fancy, though some basic forms and architectural themes have been retained.
The islands have been ravaged by several hurricanes in the last 10 years and this experience has shown up the need for building designers and constructors to improve their skills so as to provide the nation with housing stock which is as varied and attractive as ever but much more resistant to natural hazards.
St Kitts and Nevis suffered considerable loss during a 1928 hurricane. Over the ensuing 60 years or so the islands took no direct hits from passing hurricanes. Hurricane-resistant design and construction techniques were therefore not on the minds of most home owners and builders. This streak of good fortune came to an end in 1989 when Hurricane Hugo passed over the islands causing much damage to buildings. Hurricanes Luis and Marilyn followed in 1995 and Hurricane Georges in 1998. In each case significant damage was done to houses and other buildings, moreso in St Kitts than in Nevis.
This paper takes a look back at the development of the building industry in St Kitts and Nevis, discusses the weaknesses exposed by the hurricanes of recent years and looks ahead to measures which must be taken to improve the quality of constructed facilities on the islands.
The combined land area of St Kitts and Nevis is 104 square miles. The population is 39,529 (mid 1999). This is mostly distributed in towns and villages located on or near the coastline. In 1991 the Federation’s housing stock stood at 12,066 homes - 9,370 in St Kitts, 2,686 in Nevis.
The two islands of the northern Leeward Islands group are of volcanic origin. In general, the land slopes gently at first up from sandy beaches then more steeply up to the mountain peaks. The mountain slopes are well forested. In the case of St Kitts the lower slopes are extensively cultivated - mainly in sugar cane. These hillslopes are furrowed by many gullies which are normally dry but which carry considerable amounts of water down to the sea during and after heavy rains. Locally these gullies are called "ghauts".
Average air temperature is about 800 F throughout most of the year. Rainfall is around 53 to 55 inches per year.
The soils on the greater part of St Kitts are broadly classified as silty sands. These are firm and naturally well drained. On the eastern end of the island the soils are shallower and contain some clay.
On Nevis the surficial soils are clayey and quite stoney. Sands are usually encountered within 6 feet from the surface. In some areas a layer of relatively hard, sandstone-like material, usually not more than a foot thick is also encountered within this zone. Locally, this is referred to as "reef".
On both islands the soils provide adequate support for the shallow foundations of residential, institutional, commercial and industrial buildings.
[*Source: Eastern Caribbean Central Bank] The 1999 figures for the economy of St Kitts and Nevis show a Gross Domestic Product at factor cost, in current prices, of EC $682,470,000 - a per capita GDP of $17,205. The strongest sectors of the economy are:
Sugar cane cultivation and sugar manufacturing take up nearly all of the arable land on St Kitts but account for only 1.97% of the national Gross Domestic Product.
In terms of foreign currency earning power in 1999, tourism accounted for EC $190,000,000 and sugar EC $77,500,000 (representing 22% of export earnings). In 1999, there was a trade deficit of EC $313,390,000.
The early "small house" of the common folk in St Kitts and Nevis was a timber structure of compact form, either square or nearly so, with a moderate opening-to-wall-area ratio.
The roofs were pitched at 4 on 12 or 5 on 12, were either a hip or a gable design and were covered with corrugated metal sheeting of the 8/3 profile, popularly called "galvanize". These roof sheets were nailed to the roof boarding and the nails were clinched on the under side of the board. Roof overhangs were very short. Wall openings were secured by hinged wooden doors and windows fitted with wrought iron hooks and eyes. (Photo 1)
The walls were of wood stud construction covered by 1 inch nominal boards. As a variant of this, these boards were sometimes covered with wood shingles or asphalt-based roll roofing, popularly called "ruby-roy". For racking stability the houses relied on diagonal corner bracing in the plane of the wall and sometimes also in the plane of the roof (Photo 2). The longer exterior wall was broken up and braced by interior partitions.
To avoid being flooded by heavy rains these houses were usually set 2 or 3 feet above ground. The flooring was timber planking over joists set onto a sill which was itself fixed to stone masonry piers, later upgraded to concrete piers, which formed the foundation.
Wood member connections were secured by wooden drift pins or mortise and tennant joints.
These houses were very stable and secure and very well suited to resisting hurricane force winds. Many of them are still standing around the towns and villages and the rusting "galvanize" still in place on the roofs is quiet advertisement of the fact that the hurricanes which passed over the islands in recent years have left these houses intact.
As time passed and people were able to build larger houses the same basic form persisted. In some cases all that happened was that the floor area got larger. But in many cases the preferred technique was to build the basic pitched roof structure and then attach a mono-pitch or "drop-shed" section. This drop-shed section was sometimes added at the front of the building only and at least part of it would form a verandah (Photo 3). In other cases the drop-shed was added at front and back on the two long sides, creating a quite distinctive looking structure. (Photo 6)
In some variants of this style the pitch of the roof is steepened and the drop-shed is added at the shorter gable end instead of or in addition to the longer side (Photo 4). A less popular variant of the pitched roof style was to have twin gables.
Perhaps these styles developed out of a need to keep the size of the individual roof within manageable limits as far as constructiblity was concerned. Or it may be that many of these houses were actually built up by adding sections, many years apart, as funds became available.
These newer structures are also of timber construction with the popular "galvanize" roof covering. Front verandahs are extremely popular. Glass sash windows became fashionable. These are wood-framed, single hung, sliding sashes which were protected by the traditional hinged shutters.
Two-storey houses of this period are interesting. The upper story is of timber construction in exactly the same style as the single-storey houses but the lower storey is of stone masonry construction. Typically, these walls are about 2 feet thick and consist of 2 curtains of cut and shaped stones packed with mud. Joints are finished with building lime. The walls are unreinforced. (Photo 5)
This type of building was popular in the commercial sections of towns and villages where store owners lived above the store. Many of them still exist and are in good condition though occupancy on the upper floor has changed from residential to commercial.
Over the years timber construction has given way to reinforced concrete and concrete block except at the roofs which are still light-weight roofs constructed of timber framing members.
Residential structures got larger as a result of the improved economy but the basic form of the buildings was essentially unchanged in that builders and home owners simply switched materials (Photos 6 and 7). Asphalt and fiberglass roof shingles became very popular though they did not replace the metal roofs. Also, metal louvre widows, popularly called "miami louvres" became very popular. Even glass louvre windows were used.
Foundations are typically reinforced concrete strip footings under the walls. These vary from 18 inches to 24 inches wide and are 9 to 10 inches thick. The reinforcing is usually 2 or 3 half- inch diameter bars longitudinally and same size bars transversely at intervals to match the foundation concrete block wall reinforcing, the spacing of which varies from 48 inches in older houses to 32 inches and sometimes 16 inches. The wall reinforcing is anchored in the footing. The walls are hollow concrete block construction. Block cores carrying reinforcing steel bars are concreted. (Figure 1)
Usually the foundation blockwork is 8 inches thick and the superstructure blockwork is 6 inches thick. Blocks are laid in 1:4 cement/sand mortar. Building lime is not added.
The concrete floors are usually 4 to 5 inches thick and are reinforced with welded wire fabric. The floors are ground supported on compacted fill material. Usually they are detailed to extend over the top of the foundation wall.
The walls are capped by reinforced concrete ring beams. These are typically reinforced with 4 ½ inch diameter bars longitudinally and 1/4 inch diameter stirrups spaced at 8 inches on centre nominally. Also, the wall blockwork is broken at intervals by the construction of reinforced concrete wall "stiffeners" which are columns set in the plane of the wall. These are typically reinforced with anywhere from 4 to 8, ½ inch bars longitudinally and 1/4 inch stirrups at 8 inches on centre.
Roof framing members are treated pitch pine, which is a category of SouthernYellow Pine.
The rafters are nominal 2 inches or 3 inches wide lumber, usually 6 inches to 8 inches deep. Traditionally, these rafters were fixed to a timber wall plate laid on top of the walls. Fixing was by toe-nailing but more recently by hurricane clip as well. The wall plate is anchored into the ring beam with bolts at something like 3 to 4 feet centres.
Somewhere around the 1960's the method of anchoring the rafters to the concrete ring beam began to change. The wall plate was abandoned and the rafter was cast into the wall above the ring beam and anchored to it. After the rafter is positioned and before the concrete is placed a ½ inch diameter rebar is threaded through holes drilled in the rafters. This bar is then held down by rebar hooks which come up from the ring beam. (Figure 2)
This method of anchoring the rafters has 2 main advantages. It presents a much more attractive finish at the eave both outside and inside. It also seals this area quite effectively, thus preventing bats from nesting in the roof.
There are also 2 major disadvantages. When rafters deteriorate and have to be replaced, it is necessary to break into the wall to remove them. Further, there is evidence accumulating that although the anchor holds very well against the fierce uplift generated on the roof by hurricane force winds, the rafters tend to split right at the anchor point allowing the top portion of the rafter to be lifted off with the roof sheeting, leaving the bottom portion of the rafter securely in place.
This anchoring method is therefore receiving much reappraisal. The feeling is that some sort of strap which goes over rather than through the rafter, is preferable.
Once the rafters are anchored, the ceiling board is laid over them. This is usually a grooved plywood, 5/8 inches thick, nailed to the rafters. 1 x 6 tongue and grove wood is sometimes used as a variation. If metal roofing is to be used, wood purlins are installed to receive the sheets. 1 x 4 rough, 2 x 3 and 2 x 4 nominal lumber, laid on the flat side, are ordinarily used at spacings up to 3 feet centre to centre. The roof sheets are then nailed or screwed to the purlins. If shingles are to be used, the purlins are omitted. Roofing felt is laid on the plywood and then the shingles are nailed on. Typically, 4 nails per shingle are used. At the present time there is much debate over whether the plastic tape which covers the asphalted tab at the top of the shingle should be peeled off just before the shingle is laid. It seems reasonable that this strip should be removed to aid adhesion of the shingles but some builders hold that this is contrary to the recommendations of the shingle manufacturer. These recommendations are being clarified and appropriate improvements will be made to the fixing details.
None of the roof nailing is clinched.
Flat roofs are few and far between. Where they do occur they are of the built-up roofing type mostly. There are two apartment complexes in which the buildings have concrete roofs.
Parapets have not been terribly popular. Where they do occur they tend to be on the gable ends of the roof rather than at the eaves.
In the last 20 years or so the house designs have become more creative.
Plan configurations are often not box-like, as before, and roofs have become more complex in the sense that they incorporate multiple hips and gables in various arrangements. In some cases, roof slopes as flat as 2 on 12 were also used. However, the basic construction of the roofs and walls remains the same in terms of materials used and attachment details employed. (Photos 8 to 17)
During this period, the hinged, wooden window shutters went out of style, particularly in up-scale residences. The new style windows are metal-framed, either glass awning or glass sash without shutters. Typically, these windows are kept in position in the walls by the mortar which is used in framing them into the walls. Pins and screws into the surrounding blockwork are not normally used.
During this period also there has been an attempt to introduce system buildings in to the local housing market.
A Government-sponsored "low income" housing project in the 1980's employed a shotcreting technique to construct the interior and exterior walls over plastic or wire reinforcing mesh. At first, a roof of similar construction was used but this soon gave way to the traditional timber-framed, metal sheeted roof.
Just this year the Insteel, 3-D building system was the preferred method of constructing a 1,500 square foot, two storey building in Basseterre (Photo 18). This system also makes use of the shotcreting technique to construct the interior and exterior walls. Two curtains of galvanized wire mesh are used and these are coated with concrete over a core of expanded polystyrene, thus forming load-bearing wall panels. (Figure 4)
Structural steel framing, although popular with regard to industrial and commercial building construction, has not "caught-on" in the house construction industry.
Industrial buildings in St Kitts and Nevis are all of the pre-engineered steel frame type. Reinforced concrete frames have not been used. (Photo 19)
These buildings typically employ rigid portal frames spanning up to 100 feet and laid out with bay spacings up to 25 feet. Roof purlins span between frames and carry the corrugated metal roof sheets which are attached with self tapping screws. In the earlier buildings the purlins have not been galvanized and severe corrosion problems have been experienced. In the newer buildings galvanized purlins are specified. In spite of this the eave purlins in some locations have a useful life of only 10 or 12 years.
A few of the industrial buildings have metal sheeted sidewalls but for most of them the sidewall is reinforced concrete blockwork 6 to 8 inches thick.
The foundations under these walls are reinforced concrete strip footings. The steel columns are set on reinforced concrete spread footings and column base tie rods are provided.
In the earlier buildings 26 gauge roof sheet material was used. Many problems were experienced as a result of deterioration at fastener holes and buckling of the sheets under maintenance loads. The current trend is towards stiffer, 24 gauge sheets.
Roof slopes vary between 1:12 and 4:12 and some designs incorporate generous roof overhangs as well as vent blocks at the tops of the walls in an attempt to maintain the indoor temperatures at a reasonably comfortable level. (Photo 20)
Primary School Buildings in St Kitts and Nevis are generally one of three structural types.
Roofs of the type 2 buildings are generally to a flat slope - about 1:12. Roofs and side walls are insulated. These panels are constructed of 2 or 3 inches thick insulating materials sandwiched between inner and outer metal sheets.
Roofs of type 1 and type 3 buildings are pitched anywhere from 2:12 to 5:12 and are also metal-sheeted, though not insulated (single sheet construction). Type 1 roof supports are either rafters at 24 to 32 inches on centre or trusses at fairly wide spacings, perhaps 10 feet. (Photo 23)
All of the buildings have covered corridors on one or both sides. They are usually laid out as individual rectangular blocks arranged around a courtyard. (Photo 24)
Typically, the widows are the "miami louvre" type and do not have protective shutters. Some buildings have fixed, wood louvre windows which can be opened and pinned back against the walls (Photo 25). At some buildings, windows have been abandoned on the side with the covered corridor. Instead, large vent block panels have been constructed (Photo 24). This is in response to problems of vandalism and low maintenance. If these vent block panels are not shuttered in advance of an approaching hurricane, the building is presented to the wind as a "partially enclosed structure" and higher roof suction forces are induced. This is, of course, an unfavourable situation.
Where primary schools are now under construction in St Kitts the Government has decided to use metal-framed sash windows with panes made from the new polycarbonate material. This takes out the need for protective shutters.
The doors to these buildings are either solid wood panel doors or hollow core aluminum doors. Usually, they are pinned on the strike side at the lock position only. Top and bottom bolting for increased security against hurricane force winds is not the norm although consideration is just now being given to this detail.
These buildings are usually long and narrow, with a considerable area of the sidewall removed for door and window openings. Racking stability in the longitudinal direction has to be assured by rigid frame action of the steel or reinforced concrete members or by a sufficient length of concrete block wall. In the transverse direction the classroom separator walls are usually capable of acting as shear walls. Where these walls are further apart, say in laboratories, care has to be taken to ensure that the structural system provides for transferring wind loads from the roof and sidewall to the shear wall.
The metal roof sheeting used is typically galvanized steel, 26 gauge and 25 gauge. In very recent times this material is also factory-painted in various colours. PVF2 coating is commonly specified.
Reinforcing bars are of carbon steel to British or American standards. High tensile strength (60,000 psi) deformed bars are used except for 1/4 inch bars, which are smooth.
At present there are ready mix concrete suppliers on the islands. The concrete can be mixed at the plant, trucked to the construction site and delivered by remote-controlled pump at the required locations in the work. Concrete with 28-day cube strengths of 3,500 psi are normally used. But traditionally, the concrete was mixed on site using the old volumetric ratios method such as 1:2:4 (one part cement, 2 parts fine aggregate, 4 parts coarse aggregate). These proportions also gave strengths in the 3,000 to 4,000 psi range when the amount of water added was strictly controlled. Somehow, strengths for site mixed concrete in Nevis, using the same mix proportions, were lower, but strengths as high as 6,000 psi are now reported by the ready mix supplier there.
Coarse aggregate in St Kitts is produced at a Government-owned quarry. The material is basically igneous rock and it meets the requirements of the ASTM standards.
Fine aggregate is mined in the ghauts (gulleys) around the island. It is a mixture of finer and coarser sand particles and most of it also meets the particle size distribution limits of the ASTM specifications. This material has traditionally produced concrete of acceptable strength and durability.
Over in Nevis the situation is that fine aggregate for making concrete has traditionally been taken from the beaches but this practice has now been discontinued. Coarse aggregate is produced at several quarries on the island. These quarries also produce "crusher dust" which is used as the fine aggregate in the concrete mix. To augment this local supply, some fine aggregate is imported.
In the last few years the trend on both islands has been to import at least some of the concrete aggregate, both coarse and fine, from sources in Dominica, and Martinique.
Concrete blocks are manufactured at a single, modern facility on St Kitts which supplies both islands.
In St Kitts and Nevis there are no municipal sewage treatment facilities. Domestic sewage is typically handled in two separate streams, namely night soil and sullage or grey water. Night soil either goes directly to ground in the sizeable number of privies which are still in use or is treated in individual double-chambered septic tanks from which the effluent is disposed of in soak pits. These are usually 12 to 20 feet deep. (Figure 3). 20 percent of homes in St Kitts still have privies. In Nevis, 40 percent of homes still have this system.
All other household waste (sullage or grey water) is mostly discharged directly to the street drains although there is now a noticeable trend toward piping these flows directly into the soakaway.
Once discharged into the street the grey water makes its way in open surface drains, which also carry storm water run-off, through the towns and villages and into the ocean.
Exceptions to this general practice would be some of the hotels, particularly those located near beaches, the airport terminal building in St Kitts and the main hospital in Basseterre. In these cases domestic wastes are treated in on-site mechanical treatment plants before being discharged to the sea or, as in the case of the terminal building, to a soakaway.
The septic tank systems generally work well. There is now a septic tank cleaning company which services both islands. Sludge is removed in a tanker truck to designated disposal areas identified by the health departments.
In St Kitts there are some high-density areas of Basseterre where there simply is not enough space available for proper construction of septic tank systems. As a result, home-owners are forced into locating these systems under the houses - which is, of course, undesirable. This situation is not prevalent.
Soakaway problems occur in some low-lying sections of east Basseterre where the water table is not very far below ground. Soak pits do not always work efficiently because of inadequate soaking capacity. This causes problems with backed-up water closets and occasional instances of effluent seeping to the surface of the ground.
In Nevis, the clayey and stoney nature of the soil makes construction of these facilities more expensive. Large boulders have to be broken up and removed and the pit has to be taken down until sandy soil is encountered below the clay. Soaking is then quite satisfactory.
Storm water run off in towns and villages is collected at roadside and taken away by standard slipper drains. Most rain water is taken down to the sea in this manner. At street intersections the flow is taken underground briefly in culverts but a transition is made back to slipper drains at the far side of the intersection.
One noticeable exception is the eastern side of Basseterre within about 300 feet of the coast where the land is very flat. Flows in this area are conducted to the sea by concrete box drains which were for many years open at the top but have now been covered.
The best information available is that maximum basic wind speeds affecting St Kitts and Nevis in recent years were just under 100 mph averaged over 60 seconds. This means that so-called "design wind speeds" were not exceeded. The level of building damage sustained is therefore cause for concern.
Damage to Buildings and Infrastructure from Recent Hurricanes (Luis, Georges, Lenny)
|
Category |
Damage estimate $US (Source: NEMA) |
|
Housing |
246 M |
|
Commercial buildings |
29 M |
|
Institutional buildings |
64 M |
|
Infrastructure |
58 M |
In general, the newer timber buildings did not perform well in the face of the hurricane winds. Many of them were simply flattened (Photo 26). Some others were torn from their foundations though remaining largely intact (Photo 27). Where there was mixed construction, the concrete block section survived but the timber section did not. Inadequate connections between components was seen to be the main deficiency.
In the case of concrete block houses, the main category of damage was to the roofs.
The lightest roof damage was the stripping away of asphalt and fiberglass shingle or metal roof sheet. This allowed lots of water to enter the houses through joints in the roof decking.
Greater damage occurred where not only the roof sheeting but also the plywood decking was removed. (Photos 28, 34)
The most severe damage suffered was removal of the roof sheeting, purlins and plywood decking and splintering of the rafters (Photos 30, 32). Open verandahs were shown to be very vulnerable. Many were demolished. At one of the primary schools on St Kitts several of the timber roof trusses were dislodged from their supports at the top of the wall, indicating a deficiency in the original anchorage. There were not many cases of buckled ring beams or busted walls. Nor were there any cases of structural damage due to flowing storm water run off, though some residences suffered loss due to flooding.
Some houses were also damaged when Hurricane Lenny passed in 1999. This damage was restricted to properties located near to the sea shore. Failures occurred when foundations were undermined and when walls were actually battered by the crashing waves. (Photos 37 & 38)
Industrial buildings suffered loss of roof sheeting, mainly, but there were also incidences of buckled walls and purlins (Photo 33). Some of those purlin failures were clearly precipitated by loss of metal due to corrosion.
Over the last 10 years awareness of the potential for windstorm damage has increased significantly.
The pitch of some roofs has been raised in the rebuilding process and roof overhangs are now generally much shorter - 1 foot or less (Photos 35, 36). Shingles and metal sheeting have been replaced using increased nailing (6 to 9 nails per shingle) and metal sheeting screws are replacing nails. Hinged, wooden storm shutters are now reappearing either as retrofitting work or as an incorporation into new construction. (Photo 35)
Verandah construction has been upgraded by beefing up rafters and closing the purlin spacing. In some cases, home owners have elected to separate the verandah roof from the main roof, so that loss of the verandah roof would not precipitate loss of the main roof as well. Others have gone one step further and are now not only separating the verandah roof but also constructing it of reinforced concrete.
And in general greater attention is being paid to the details of attaching the roof sheeting and shingles, of tying down the rafters, and of anchoring the lighter timber houses to their foundations.
Plans for new construction or for renovation of buildings are traditionally reviewed by the St Christopher Building Board in St Kitts and the Nevis Building Board in Nevis. In recent times 2 other Building Boards were added in St Kitts. The Frigate Bay Development Corporation which regulates building activity in the Frigate Bay area and the Southeast Peninsula Land Development and Conservation Board which does likewise on the Southeast Peninsula. Construction industry professionals are usually represented on these Boards, as are the Health Department, the Electricity Authority and the Planning Department.
Successful review of the plans leads to issuance of a building permit. Construction is then monitored by inspectors employed either by Government or by the Boards.
At this time these Boards are being reconstituted under new development and planning legislation but traditionally the Boards and the inspectors have had the necessary legal powers to cause unapproved construction to be stopped.
Most small buildings on St Kitts and Nevis are constructed by companies or informal work groups which are headed by tradesmen who have moved up to management and ownership positions. They are not usually graduates of a technical school. At present, less than about 10 percent of construction workers have attended the local vocational technical schools. The number of graduates turned out annually by these schools is only about 16. On both islands right now most of the Government-funded "affordable housing" construction is being undertaken by just such informal work groups.
On the design side, there are no less than 17 practicing architects and engineers in the Federation but most small buildings are designed by drafters who have worked in an architect’s or engineer’s office for some time and have built up considerable know-how in this area.
At present, the construction field is unregulated. Neither designers nor constructors are required to be licensed or registered or to have had any particular level of education, training or experience. It will take considerable political will to bring about a change in this state of affairs but the local Contractor’s Association is in favour of such a move and has made representation to Government on the matter. Some home owners also are known to favour such registration. The local Engineers’ Association is currently dormant and there is not an Architects’ Association on the islands. Consequently, a united designers’ voice is not currently being heard on this issue.
A Building Code for St Kitts and Nevis has been drafted and is now the law of the land. At the present time, the Code is not yet in print and available for study by prospective users of the document. (Since this was written, the Code has been printed and made public)
Qualification-based registration of designers and constructors will undoubtedly have a positive impact on the quality of construction.
Improved quality of constructed facilities would also result if designers, inspectors and constructors, whether registered or not, become increasingly sensitized to the principles and practice of hazard-resistant design and construction and if the traditional attitudes of antagonism between inspector and constructor are replaced by a spirit of genuine professional collaboration between the parties. It is also important that there be a sufficient number of inspectors to properly cover the on-going construction activity.
The introduction and enforcement of the Building Code will also be a positive force for improvement in the quality of construction in the Federation.
| USAID/OAS Post-Georges Disaster Mitigation: http://www.oas.org/pgdm | Page last updated on 10 Sep 2001 |
