Insulation and the like

Wed 25 Mar 2009, 17:00

Mark, I don't know your house, but there can be dangers in trying to make old houses too airtight.
Extract fans if you have them may not work properly if you don't have trickle vents because it is harder to draw air in.
If you have solid stone or brick walls, because the internal humidity could be increased because of insufficent air changes, you could increase the risk of condensation and you could get mould growth in corners and round window reveals and water running down the windows if they are single-glazed.
There could be consequent respiratory problems and more risk from radon gas (the second biggest cause of lung cancer in UK). So it becomes more important how you deal with intentional ventilation as distinct from unwanted ventilation.

Wed 25 Mar 2009, 16:27

Curtains are also a useful heat-saving measure Liz. Walking through the middle of Charlbury on my way home from the station in the evening several times recently I have been struck by how many people have their lights on but the curtains undrawn. No doubt the heating is on at the same time so all that lovely warm air is escaping through the windows. If the curtains were drawn the heat would be retained much better.

Tue 24 Mar 2009, 07:11

I think that draughtprofing might have a bigger effect than we assume. UK homes have not generally been well built and on average (across all the stock) they suffer from 14 air changes per hour. That's a lot of waste heat which will be especially bad if it's windy. When people open their windows to let in fresh air, they are usually also letting warmed ari escape. And the air in a room will be freshened quickly, yet people leave windows open all day.

It may not be possible to deal with the kinds of draught caused by poor building practices. But where you can - insulating under floorboards for example - it can make you feel significantly more comfortable so you can turn the thermostat down, and that saves energy. But everyone can check doors, windows and keyholes. Mark Evans, Charlbury carpenter, is very good at re-fitting door and windows to remove draught.

I suspect that Mark was looking for Lower Watts House. That was built to make it airtight - we achieved 2.5 air changes per hour. New homes built under Building Regulations 2006 are still allowed to build to 10, but that will be coming down rapidly with proposed new regulations that will come into force in September 2010. New very low energy homes are built to less than 1 air change per hour. Fresh air is then provided through mechanical ventilation with heat recovery to deal fresh air in the right quantities to the right places when you want it.

The new community centre at the Spendlove will be built to that very high standard.

I think

Mon 23 Mar 2009, 11:39

I do not think there is a problem overlaying your existing insulation with Thermafleece but please take advice from info@secondnatureuk.com. Don't forget to insulate the loft hatch.
I does sound as though you should install either tile vents or soffit vents or both to cure the condensation problem though. A good builder should advise you on the easiest for your particular situation.
Good draughtproofing will make the house more comfortable and will have a marginal effect on your CO2 emissions. Re your light and wiring, please take advice from an electrician. Ceiling lights could overheat if you cover them with insulation, and electrical wiring could overheat if the cables are near their maximum loading (which is unlikely).

Mon 23 Mar 2009, 11:13

Thanks Reg and Jon.

Reg, do you think the existing 100mm of rock wool should be removed if using something like thermafleece, or can it just be laid on top? Even with existing insulation there is considerable condensation on the roof underlay in winter, which drips onto the floor, so sounds like there is a ventilation problem.

Sun 22 Mar 2009, 23:57

Thermafleece has a slightly better thermal performance than the well known rock wool alternative and has less embodied energy. You need to aim for a heat flow rate (U-value) of about 0.18 W/sq.m./K which means about 100mm between the ceiling joists and about 150mm above the joists. Thermafleece will give you 0.16 W/sq.m./K
You do need to be a little careful though because by making the loft space colder you should watch pipe and tank insulation, and if the loft space is not ventilated there is a danger of condensation on the underside of cold underlay felt if it is not the breathable variety.

Sat 21 Mar 2009, 12:36

We got ours done quite cheaply (well under £200) and efficiently. Have a look at www.westoxon.gov.uk/environment/envhealth.cfm and follow the links.

Sat 21 Mar 2009, 11:27

We need to increase the insulation in our loft, has anyone got good experience of someone who can provide advice and installation? Nervous of doing it myself because of electric wiring, recessed lights etc.

We're interested in using a natural product like Thermafleece, anyone got experience of that?

Finally I remember reading about someone in Charlbury who had draught-proofed their house to a very high level, does anyone know where I can get information on that?