Tuesday 22 November 2011

Mind the gap!

This is a pretty good mantra when insulating anything, as there should be no gaps.

The concept of insulating the extension and existing ground floor with 300mm sheets of insulation sounds simple enough, but actually doing it is not necessarily quite so straightforward..

To prevent air pockets between the boards, they were placed at least 6mm (but no more than 15mm) apart so that expanding foam could be squirted into the joints. The foam caused the boards to lift up as it expanded, so next job was to place blocks on the top to keep the boards in position.


It might have been easier to use 2 layers of 150mm board instead of the 300mm boards, but any dirt between the first and second layer of insulation could introduce another set of air pockets. Maybe  interlocking insulation boards would have been more user-friendly and give a better end result.

The up-stands and down-stands of insulation are not without their difficulties either. Making a neat job with no gaps is important, and requires some care to keep the insulation layer continuous and tight up against the wall.

Up-stands need to be stuck down (with foam or tape) before the concrete is poured - or you get a cold bridge where concrete fines flow into the gap. Our builder suggested that it might be easier to place longer up-stands and place the main horizontal layer of insulation inside them - a good idea, but the insulation was already on site, and not in the right combination of sizes to fit that approach.

These are the things you only know when you've tried it. The main thing is that the insulation is placed as carefully as possible to avoid gaps, and foamed or taped before concrete is poured on top. It isn't rocket science, but it can be a pain.

Most builders will think this super-insulation lark is completely crackers - it is very over the top by comparison with current building regulations. However, if we want a house that needs virtually no space heating, these details matter.

Monday 14 November 2011

Preparing the ground floor for insulation

While the builders are getting the extension ready for some serious under-floor insulation, Richard has been busy doing something similar for the lounge.


Step 1 - remove floorboards carefully (for re-use as the attic floor when the loft conversion happens)



Step 2 - Richard admires his handiwork...and notes interesting arrangement of joist ends close to fire place but unsupported!

Step 3 - remove joists (for re-use as raised beds)

While it would be possible to insulate between the existing joists, we're removing them to make way for 300mm of silver EPS with a solid floor on top.

Saturday 12 November 2011

Windows ready to ship.

We ordered the windows well in advance, knowing that on similar projects the windows have held things up (either due to long lead times or unanticipated delays).

However, we are now in the opposite situation - our passive house suitable windows (EcoPassive from Green Building Store) are almost ready to go, and should be with us in early December. But we've got a few other jobs to complete first, including the small matter of rebuilding the roof!

For a smallish house on a narrow plot, this house has a lot of windows - so now we need to figure out where to put them until each one is ready to install. There is also a lot of work going on both inside and outside the house, so they won't be stored on site, methinks.

Thursday 10 November 2011

The first energy-efficient product arrives

The extension is starting to grow, and thanks to careful arrangement of the various blocks, we should lose virtually no heat from the extension into the ground via the external walls.

The foundation and first 4 courses of blocks are standard (to get us up to the required height as the house is higher than the garden).

Above that we have a row of highly insulating Marmox Thermoblock (the ones with the stepped edge), and then normal insulating blocks above that.



Tuesday 8 November 2011

We have a footing!

Happily, the weather has been mild so we now have a footing for the rear extension. By the end of the week we should have some fancy insulating blockwork up to the dpm, rapidly followed by a hefty amount of silver EPS before the solid floor.

The boys liked watching the digger best....