of architects and engineers

Today we had the first visit by Martin one of our Structural Engineers. Martin is looking after foundations and the basic structural integrity of the building. The other, Ted, is specifically looking at the roof structures and the SIPS engineering as it is very specialised. More of Ted anon. Martin spent about half an hour on site and another hour and a half with us looking at the plans and discussing various details. He wants the founds to be in a 200mm concrete ring beam as the depth of aggregate under the floor slab is over the 600mm recommended by NHBC. We need this for thermal mass, otherwise we would have a timber suspended floor.This 600mm thing is a rule of thumb rather than anything hard and fast but it might actually suit us to put in a ring beam and lower the levels by 10-20cm as it will reduce the amount of aggregate fill and hence save us money. Anyone who can save us money by design is okay with us. We are on a fixed budget and more aggregate means less stained glass, or fewer elm work tops etc, - those wee finishing touches which we are aiming for with a vengeance. The drop in ground level on the plot means a maximum fill level of 1.5m so a ring trench locating bedrock levels is worth investigating. It will also begin the excavations for the strip trench for the founds so is ‘a good thing’. However we want to be able to see the horizon so a lowering of the floor levels has to be balanced against our view - which I am sure you will agree is just amazing. Another alteration Martin thinks is necessary is to revert to timber frame for all internal walls as the proposed blockwall will be too slender for its height and well outside the slenderness ratio recommendations. In plainwords it will be unstable and have a tendency to fall over. Again this change back to timber frame might be a good thing though the block wall would have added to the thermal mass and also helped solar gain in the open plan living area transmit through to the bedrooms. Martin was in agreement that our thoughts on rim joists for the gallery area would work in practice. Now Ted is mostly ‘doing the roof’. We have changed the main roof from 12 to 24 facets on his advice and he also has a thing about elegance and feels it would be aesthetically more pleasing. This is a good thing as engineers are usually more functionally minded and architects more aesthetically oriented. It is the engineers job to make the structure work in practice and ensure that the architects ideas are actually buildable. This is another good thing. Our engineers both like the design and that it is innovative and are very very helpful as a result. Engineers are generally more pragmatic and practical than architects though Robin has tried hard to consider the ease of building and help us look for solutions. Sometimes these are rather expensive and outside our means so we have to look for cheaper ways of solving design problems. As we are doing something quite new in having an unsupported roof in SIPS then it is worth the extra money on the engineers as we do want our house to stand up - preferably without creaking ominously especially in a Hebridean gale. The turf roof complicates matters for Ted as it is a heavy roof and the loadings are increased. Also the top surface of the SIP is not vented and the architect and engineers all feel we need to vent it to prevent a condensation risk and our roof rotting from inside. I am very miffed at this second skin as it defeats the object of having a turf roof on top of the SIP - we now have to introduce 50mm battens and another layer of OSB to provide the ventilation space. A real pain as SIPs are supposed to be moisture barriers and my solution of placing another vapour barrier internally to prevent an egress of moisture through the roof SIP was considered inadequate. As always there is an upside as it will improve the thermal performance of the roof.

These are some of the every day things we think about and discuss with the professionals who are helping us. We don’t always agree but all of us seem to be pretty much problem solving oriented and ultimately that is what we are paying them lots of money for.