A self build house project diary
by Oliver Cannell

Boarding out and insulating the roof

Hopefully we can get the roof on and watertight before any bad winter weather arrives.

Mostly, the boarding-out of the roof trusses has been a quick process. This was especially true of the roof section at the back of the house, as there is only one large expanse of roof, which comes down to meet the central flat section.

However, the unusal shape of the adjoining edges, has slowed progress a little. As the central section is flat, the carpenters have built a shallow pitch into the structure - just enough to enable rain water to run off at either end of the house, into the guttering.

With the additional factor of having a change of direction in the front roof section, the final result of the first plywood layer looks great - it's almost sculptural in the way all the surfaces flow into each other from multiple angles.

Insulation layer

On top of the plywood skin, there is a vapour barrier of thin polythene and then 100mm Celotex insulation foam sits on top of that. I know this style of insulation if very effective at providing a great heat loss barrier but I'm sure the manufacture of it is quite horrific (although I actually know nothing about this yet). I'm sure it doesn't involve ozone-layer damaging gases being expelled into the atmosphere - in the way that polystyrene foam used to be in the old days (the 1970's and 80's) - but I'm sure there must be a more eco option to this stuff.

As there is no facility available in this country (globally?) to recycle it, the need to keep waste to a minimum is essential - otherwise it's all going into the ground as landfill. Obviously builders will mostly look at the financial side of this product, with regards to avoiding waste, as it's quite expensive to buy. But we should always look at the ecological effects of the building materials we're using, both in their manufacture and in the disposal at their end-of-life.

The offset of this, of course, is how much benefit these insulation products hold over other methods. All in all, the house we're building is going to be very efficient and (so I'm told) the running costs will be very low. I'm looking forward to having a nice warm home with minimal fuel bills. So this means much less burning of fossil fuels from power stations - although it will be nice to use more eco power sources in the future (such as from Ecotricity or any other eco energy supplier).

Final boarding layer

On top of the insulation, is a final layer of boarding. This is made up from OSB (Oriented Strand Board) and is screwed down directly into the plywood boarding layer below. The OSB will also be built up-and-over the block-work at the front and back of the house, to create a 'tray' in which to sit the sedum roofing system, once we get to that stage (sometime in the future). The rubber waterproof membrane will eventually be secured on top of all this OSB layer.

More details and photos of the roof construction, later.

Next entry: Connecting to the outside world - water, gas and electricity (Wednesday 12th November 2014)

Previous entry: Main roof structure is all done and looking great (Tuesday 21st October 2014)

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