COST BENEFITS

In this industry we hear much talk of ‘total build costs’ which is often the first line of defence for manufacturers trying to justify expensive products. One possible saving is on the foundations because SIPs is a lightweight structure with uniform load distribution. Sometimes there are cost benefits in off site fabrication and sometimes there aren't and this may vary from site to site and also be weather dependent. The intention is always that site labour costs are reduced but the big question is whether they are reduced enough to compensate for the sometimes significantly higher cost of the panels. The speed of build is compelling but you need to guarantee it will happen to a schedule which suits you the builder. The time between the slab being ready and the building being weathered in can be as little as 5 days but this assumes that you can guarantee that the over-site will be ready so you can book the delivery to follow on. If you miss the slot you are either faced with storing panels on site or rebooking. Conversely if the groundwork’s (always weather dependent) go well and you are ahead of schedule you well may lose all that time gained waiting for your SIPs delivery. A one off masonry build, on the other hand, has a shorter supply chain and the materials are generic. In most areas of the country a quick call to the merchant for a load of blocks and some sand and cement gets you up and running. With the supply process for SIPs being more protracted the success of the project depends largely upon the ability of the suppliers to respond to changing conditions.

The on-site construction requires minimal carpentry skill but it is almost invariably dependent upon a crane or at least a JCB Teleloader so those involved need to be fully trained in working with cranes and at heights. A manually handled panel is based upon standard 1200 wide sheets but there are companies such as SIP BUILD who will supply whole elevations which can be craned into place. In most respects the build is no different to timber frame construction until you come to the roof where the large panels need to be located accurately and gently lowered into place.

Talking to builders we have heard some mixed reports concerning the build. Some smaller builders love it and others seem to have abandoned the idea of using SIPs because they have lost money on them and don't have enough control over the process. In one case the panels were delivered to site wrongly cut, though it wasn't clear who was to blame. In another case the roof followed some weeks after the main delivery which meant rebooking the crane. The advantage of having a house fabricated off site can also be a distinct disadvantage in that problems can't be readily rectified. To be fair to SIPs manufacturers there are many smaller builders, or even their clients, who seem to make it up as they go along and end up requiring very unusual structures. Brick and block certainly suits this ad hoc approach better than prefabrication. There are also niggles with SIPs such as not being able to chase out for back boxes and cable runs. If the panels are chased they lose their strength. They only answer is to pack out the plasterboard or run conduit in the insulation core. This of course means up-rating the cable to stop them cooking.

HORSES FOR COURSES

A number of larger manufacturers are reluctant to get involved in small projects probably for the reasons given above. Historically the best use of SIPs seems to have been in building simple square boxes with a mono or duo pitch roof. Larger SIPs suppliers such as Kingspan TEK have this sort of computer aided high volume production down to a fine art, as well they should. The key to success is to match the supplier to the project and talk to their previous clients where possible. Manufacturers such as North East based STAYLOR DESIGNS and SIPTEC are happy to take on more ambitious designs in the self build market. In particular the ability to keep to delivery dates is key. If the speed of build turns out to be a myth and the costs creep up then all the builder is left with is a very energy efficient house, which might arguably have been achieved in some other way.