The difficult obstacle appears to be the will to do, rather than any knowledge deficiencies.

ESP is not normally a structural (load bearing) material. It can be used as insulation sandwiched between structural materials.

However, given the improvements in building materials, if a manufacturer has been able to develop a structural foam panel, then you should request the technical specifications, and ensure that it comes with a verifiable warrantee if you wish to use it.

If you know of such a manufacturer, then you are welcome to post its web-site here so that it can be Weighed in the Balance.

The Barbados National Building Code (BNBC) allows rafters to be spaced up to 1.2 m, however, you should use the timber type, size, and span as specified in Table 2.803.9. However, if it were my house, I would not space the more than 600 mm apart.

Let me state that I am not giving you any advice here whatsoever, since I have neither seen the plans of your house, nor received information on your loading requirements. My advice to you would be to exceed the minimum building standards in the Building Code and to seek the advice of a Registered Engineer.

1. Roof

The first thing that I would do is to determine whether my roof is actually substandard. If I have a 2.4 m (8 ft) long 2”x6” Purpleheart rafter, then my 770 mm spacing exceeds the minimum requirements of the BNBC. However, a similar rafter out of Pine is less than what the BNBC requires.

I would install stainless steel hurricane connectors at all timber connections, and ensure that I used stainless steel screws or nails. I would also install rafter bracing (collar tie) and additional roof covering connections as shown in the BNBC Figure 2.805.

2. Shear Walls

If my walls are timber stud walls, then I would install a timber brace as shown in Figure 2.804.2. If they are concrete block, then I would fix a 50 mm x 50 mm galvanised weldmesh (BRC Ref.5050 25) to the external face of the widest panels that I had, and apply a 12 mm minimum (1 cement:3 sand) mortar plaster. See BNBC Figure 2.405A for a description of the wall panels.

3. Windows and Doors

I would secure my windows and doors. United Insurance has a booklet which describes some effective retrofitting measures and which can be downloaded from here:
http://www.unitedinsure.com/united.cfm?LID=helpful%20info&SID=Hurricane%20Retrofitting

I would also get adequate insurance.

The Barbados National Building Code, Section 2.507 provides the procedure for concrete slabs on ground floors. You should remove the “top-soil and any organic material” (BNBC 2.507.2 (a)).

Mud (topsoil and organic material) will compress. If you leave it in, then you can use it as formwork to support your slab, which you should design as a suspended slab. BNBC Section 2.603 gives the minimum thickness and reinforcement requirements for suspended slabs.

If you wish the underlying material to permanently support the ground floor slab, then you must remove the topsoil and organic material and replace it with granular (e.g. marl) fill.

The Code (section 2.506.1) actually recommends a minimum strip footing size of 12″ wide x 8″ thick (300 mm x 200 mm) assuming a good bearing material. The 16″ wide x 10″ thick (400 mm x 250 mm) is for a two storey building. You may wish to consider the two storey foundation size since you or your estate may wish to add another storey at a later date.

The 24″ (600 mm) wide footing exceeds the minimum for rock. If your footings are not bearing on hard limestone, then it may be prudent to use the 24″ wide footing to manage the risk. In my opinion, it is not a waste of money. Perhaps a 36″ (900 mm) wide footing for a single storey house on hard limestone could be a waste of money.

The Barbados National Building Code (BNBC) states: “Excavations for footings shall be taken down to the depths necessary to provide solid support of the loads superimposed by the building. FOOTINGS SHALL NOT BEAR ON FILL MATERIAL.” BNBC 2.504.4 (Emphasis mine)

Therefore excavate until you find the necessary solid support. If you do not find it, then you need some professional advice depending on the type of soil that you have (sand, clay, etc)

Regarding jagged edges of rock. It is good practise to cut into the rock 50 mm to 75 mm to remove the weathered portion, provide a relatively flat bearing area, and provide a key to the footing.

For budgetary reasons, you should estimate $250 per square foot of floor area. I regret to report that I cannot in all good conscience recommend any good builders. You will see why in today’s article.

Of course I must give you the standard preamble as given to Tony W in the post before yours, since I have not seen the site.

The amount of vertical reinforcement that your builder is using is normal if the wall is to retain something. Perhaps it is to retaining water from an underground water tank, or external soil because the foundations are deep.

If the foundations are shallow, and there is no soil or water to retain, then if it were my house, I would use 12 mm (1/2″) diameter high yield bars at 600 mm (2′) centres for all of the walls, not just the foundation. It is also important to fill all block cavities below the ground floor slab with grout, even the ones without any reinforcement.

The BNBC calls for a minimum of 10 mm diameter mild steel reinforcing bars at 800 mm centres. (BNBC 2.405.2 (c))

The BNBC 2.506.2 specifies minimum pier or column pad footing sizes and notes that such footings should be continuous.

Pier footings or pad footings are normally used to economically support columns. Strip footings are normally used to economically support walls.

You can probably have the roof framing and close boarding installed for around $25/sq ft. The Gypsum Wall Board is cheaper than the T-111, however, if it gets wet, it can facilitate mould growth. Please be advised that during a hurricane, if the building envelope is breached, just about everything inside gets wet. Principally for that reason, I would not use the gypsum material.

The minimum building standards in the Code are just that – minimum building standards.

I would use this slab thickness and reinforcement wherever I expect heavier loads, like my library. Where I expect lighter loads, like a bedroom or bathroom, I would keep the 150 mm thick slab but increase the spacing of the reinforcement to 200 mm (8″).

If I were uncertain about the future use of a space or room, then I would assume patio loading throughout.