Questions about insulation and draft proofing
OK. Here's something worth exploring. If you have a solid wall house and have minimised draughts as much as possible, installed double (or secondary glazing), radiator panels and keep the doors to rooms closed...how much heat can you retain in the house? What would change if you used insulating paint? Oh and have you sealed your floorboards...and if you do all this, how does the house breathe? And of course - a relative concept - how cold is cold? Having been brought up without central heating and swimming in cold water I reckon my tolerance of cold is higher than most...but can we adapt or is our reaction to temp fixed? It's a bloody minefield?
some of the public consultations on the PAAP have included input that the conservation areas should be extended. Yikes.
And maybe someone can answer this conundrum. I have insulated cavity walls. I went away for a week before xmas and came back on a relatively mild day (it had been several degrees colder earlier in the week). The inside of the house was colder than the outside temperature. Was this the insulation or what?
And can any one shed light on what the term 'emissivity' means in terms of thermal properties?
Carl
#1
All very good points, Carl and I suspect as most people dig into these issues they get paralysed amid the web of considerations.
Personally I'd just like to be able to draw up three lists (low, medium and high cost) listing in descending order of impact energy saving improvements I can make for MY particular house based on its eccentricities of build (eg my three exterior wall bathroom) and interior design choices (eg no carpet on entry stairs and landing which means that it leaks cold air like an arctic sieve). At least I'm aware of some of the issues (but confused as Carl on others in terms of their place on the list) but most people won't be as clear as I am. Sounds like a direct link to the Home Surveyor intro seminar.
Maybe one good aim for Peckham Power would be to help our good citiziens of Peckham and Nunhead draw up their own list based on clear easy info we can give them.
x
M
#2
It is a bloody minefield but hey, that's what makes it fun (I hope you can hear my tongue placed very firmly in my cheek!)
Just for geeky kicks, I'll try to answer some of your questions... I've been reading about some of this stuff over Christmas and - if you'll indulge me - this is a good opportunity to try out some of the things I've read. No idea if I'm right or not! It's a bit of a bumpy ride... I've never done these sums before...
The rate of heat loss is proportional to 3 things: 1) the temperature drop across the walls (or floor or roof or whatever), 2) the surface area and 3) the "u-value" of the walls. Solid 9" walls loose 2.1 watts of heat per square meter per degree of temperature drop (this is the "u-value"). So the large external wall in our living room looses heat at a rate of about 1000 Watts when the outside temp is -8°C and the internal temp is 18°C (2.1W/(m2K) x 18.5m2 x (18°C - -8°C)). i.e. it's like we've got a 1-bar eclectic fire running in reverse. (we rarely get up to 18 °C but this value seems to be often quoted as the "comfortable" temperature).
To put this into some context... on full-blast, our two (crappy) living room radiators kick out heat at a rate of about 2000 Watts total. So it's not hard to see why it's tricky to heat our living room when a single external wall looses heat at a rate of 1000W and the uninsulated floor and crappy double-glazed windows probably loose another 1000W (i.e. the room looses heat as fast as the radiators pump out heat).
The tiny bit of research I did on insulating paint suggests that it's a good idea it's no miracle worker. Apparently it's roughly equivalent to about 4 millimetres of rigid foam insulation. So if we had insulating paint on our solid walls then our u-value would drop from 2.1 to about 1.6 and the rate of heat loss (in the same situation as above) would drop from 1000 Watts to 750 Watts (I'm actually quite surprised it's that effective - I'll definitely give it a go).
If we installed 70mm of rigid foam insulation (no insulating paint) then our U-value would drop from 2.1 to 0.285. (A heat loss rate of 133 Watts).
70mm of rigid foam insulation + insulating paint = u-value of 0.271; rate of heat loss = 129 Watts.
So it's worth noting that insulating paint makes much more difference when applied to poorly insulated walls than when applied to well insulated walls.
There's a U-value calculator online here: http://www.vesma.com/tutorial/uvalue01/uvalue01.htm
There are two issues here: 1) letting the brick & wood breath and 2) letting the occupants breath.
Assuming you install internal insulation to a solid-walled building then you have to let the brickwork, underfloor space and below-rafter space breath to the outside. Solid-walled houses were "designed" to breath. If you glue insulation to the interior surface of external walls then they should be able to breath sufficiently through the exposed external face, assuming the external brickwork is not covered in a non-breathable finish. If you install insulation below the ground floor floorboards then you have to be careful not to fill the entire underfloor space or to block the air vents. If you install insulation between the roof rafters then you have to leave a 50mm air gap between the top of the insulation and the tiles.
For optimal thermal performance (and to reduce the chances of condensation forming between the insulation and the brickwork) the aim is to make the living space airtight (i.e. seal on the warm side of the insulation). But once you seal the living space, you have to let the occupants breath! (there was a report recently about some schools which had their air-tightness improved without any additional ventilation and it resulted in significantly worse academic performance of the pupils!) As far as I know, the best option is mechanical ventilation with heat recovery (either for single rooms or for the entire house). But you probably knew that. The hardware costs about £200 for a single room MVHR unit or about £1500 for a whole-house unit. Good MVHR units can reclaim 90% of the heat in the exhaust air. I'm thinking of installing a single-room MVHR unit in our livingroom once it's sealed. Yes, MVHR units consume small amounts of electrical power to run the fan but this is massively outweighed by the heat they recover. Whole-house MVHR units only make sense if the entire house is almost completely air-tight and well insulated.
In what context is "emissivity" used? I would guess that it's something to do with the way that insulating paints work: i.e. they reflect heat back into the room.
Yeah, I agree - good idea.
Big love,
Apologies for the long email,
Jack
#3
Hi Jack
This is really informative. Thanks so much.
M
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