Insulating the loft (part ii)

Looks like I started just in time; the weather has definitely turned autumnal, and the heating cut in this morning for the first time this year. However, the good news is that up in the loft, the temperature is cool enough that it’s actually possible to work. And in theory at least, the more insulation I get in there, the cooler it will become.

After running some errands this morning, I managed to spend about 4 hours insulating the loft this afternoon. I completed the gable dormer over our bedroom (which was completely stuffed full of trusses, making it a nightmare to work in) and about a third of the remaining area. It was interesting to see how poorly insulated the “hard to see” areas of the loft actually were; presumably because the builders found it hard to get in there, and didn’t expect anyone to ever check their work! But there was insulation that didn’t stretch right into the eaves, and some big gaps where there was no insulation at all, which clearly hasn’t been helping us to keep the house warm.

I’ve patched all the insulation between the joists, installed renovation eaves ventilators (to make sure the insulation doesn’t block the airflow through the loft and cause condensation), and then added a further 200mm of cross-laid insulation over the top of the joists. I’m not totally convinced that the eaves ventilators are making a big enough gap past the insulation; the building codes say 25mm is sufficient, but looking at the gaps, it seems pretty small, especially compared to the huge gaps that were there previously. I think I’ll be keeping a very close eye out for condensation this winter, just in case I’ve overly constrained the ventilation.

Tomorrow I need to complete the remaining two thirds of the loft space, which is all nice simple square areas, that are easily accessed. Hopefully no more than another couple of hours work. But then I also need to double-check the insulation on the pipework to the heatstore, and finally insulate the loft hatch.

The loft hatch is going to be interesting. I made this one from 20mm marine plywood, varnishing and painting it to stop it from warping. But it warped anyway, and now doesn’t form a particularly good seal, as revealed by the dust patterns on the sides of the hatch. So at a minimum I need to draught-proof it. But realistically I need to add some insulation to it too, which is going to be awkward.

At the moment I favour the idea of glueing some Celotex insulation batons to the inside of the hatch with something like “no nails”, to a depth of about 100mm … which is equivalent to about 250mm of glass fibre insulation. But to make it work well, I’m going to need to get the size and shape of the insulation exactly right, which is going to be interesting.

So far I’m pleased with progress, though clearly the ultimate proof will be in this winters heating bills.

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