Selective interior superinsulation for our timber-frame house to keep our footprint down and us warm...
2010's main project on the conservation side (as part of the aim to get the house to be "zero-carbon" for primary energy) is to reduce our gas consumption for heating.
For 2009, even given the unusually harsh winter, we managed to cut gas use from 9MWh in previous years to just over 6MWh. Some of that saving was with water heating (behaviour changes, pipe lagging), not all in space heating (ie central heating).
My strategy is to focus on maximising warmth and comfort in our living room, where most of the family spends most of each day in winter, to shave as much as another 1MWh off our current ~4MWh/y space-heating demand.
Another practical aim is that even if our power/heating fails on a cold winter's day, that room should stay comfortably warm with 3 or 4 people in it, ie from 300W+ of body heat and even without appliances (TV/light), etc.
In the longer term I want to replace the glazing, eg with triple glazing with a whole-window U-value well under 1W/Km^2. For now, our improved curtains from 2009 will have to hold the fort, possibly with extra thermal/reflective "black-out" linings... (I have been battling for months to try to get sensible quotes, but it's hard work, so it may be next year before this is resolved.)
We already used the highest-tog-rated underlay available when we replaced the carpet in 2009 (though at tog 2.3 still only ~4W/Km^2). Given the SAP report floor U-value of 0.79W/Km^2 and the underlay of ~2.3 tog (and assuming 1.0 tog for the carpet) gives us ~0.63W/Km^2 overall (1tog = 0.1Km^2/W), thus plenty of room for improvement if we can't find a way to use the floor thermal mass constructively, eg by insulating around its perimeter.
This project is to superinsulate and improve other thermal elements of the room:
We initially planned this with Kingspan Kooltherm K17, but I realised that this might be a good opportunity to test Spacetherm aerogel so that was substituted in the plans, but it was still many times the price for similar performance (>£100/m^2 for 40mm insulant) even with Proctor's generous discounts and direct sale to us, though I did take the opportunity of the improved R-value to up the spec a bit.
We ordered 5-off 2440mm x 1220mm Spacetherm-P 40mm aerogel faced with 9.5mm plasterboard on 2010/05/05 and it was with us less than a fortnight later.
The overall U-value of the Spacetherm-P should be ~0.30/Wm^2 (40mm aerogel at 0.013W/Km and ~9mm plasterboard at 0.14W/Km).
Work started 2010/07/13 and took two days to tear down the ceiling, insulate above new plasterboard, and put up the aerogel Spacetherm-P. Early on we made a couple of exploratory holes in the plasterboard of the exterior walls to check the construction, and rather than a void, behind the 12.5mm plaster is a ~0.5" fibre matt enclosed in a plastic lining, which seems in fairly good nick, eg no obvious sagging. So my U-values will be better than the 2.0W/Km^2 that I'd feared or the 0.8 that the SAP tables gave for the energy certificate; possibly closer to 0.6.
Given various assumptions about the existing wall thermal performance it is possible to estimate the performance of the superinsulated walls though thermal bridging from door/window frames and steel drywall screws, etc, will reduce overall performance:
See images of the work.
Taking down the old plasterboard, putting glass wool above it ie in the void below the plywood of the floor above (100mm, ie to about 1/2 of the 9" depth, for a U-value of ~0.4W/Km^2) and putting up the new plasterboard seemed fairly straightforward. There is a little extra packed around the microbore central-heating pipework as lagging where it crosses the living room ceiling above the plasterboard.
(The packaging claims that the glass wool is made from recycled bottles.)
The ceiling U-value may have improved from ~3 to ~0.33W/Km^2 (12mm plasterboard, 100mm glass wool, ~15mm plywood of floor above). So considerably less heat should leak uncontrolled up into the bedrooms where it is generally not needed during the day. On very cold days the radiator TMVs on their normal daytime 'frost' setting may come on a little at times, reducing central heating savings.
Note that the noggins at the exterior edge of the ceiling void were covered with reflective foil faced rigid foam (Xtratherm) up to 80mm thick (with one foil face towards the exterior).
The aerogel board seems to be tricky to work with, for example it snags an electric drill bit making it hard to withdraw, it is very hard to cut with a Stanley knife, and only an electric skilsaw seems to be effective. The builder said that as a consequence it's much slower to work with than alternatives such as Kooltherm, and with the dust being horrible too, he'd rather not work with it again!
The old radiators have been removed and the underfloor microbore feeds to them disconnected entirely from the central heating system to avoid accidents. The new living-room radiator will be plumbed directly to the boiler with 15mm pipe, and the existing/remaining two downstairs radiators will be reconnected to the old pipework directly with 15mm pipe, bypassing the old microbore.
The new radiator will be double-layer and consequently can be (less than) half the width of the single old radiator replaced.
The new radiator will be mounted on the internal wall to reduce direct heat loss through the external wall and maximise space in the room.
Plastering was done with a binding layer in corners/vertices, then two layers, and was visibly dry after a couple of days, but is getting a week's drying time total.
2010/07/18: The plastering has gone quickly, with the hot sunny weather probably helping.
We had a slight excitement when the RCD circuit breaker for the mains sockets tripped after a little wet plaster strayed near the wires for a socket, unnoticed by anyone and clearly no arching nor shocks or whatever, so it did its job splendidly!
Internal dimensions of the room surface to surface are approx 4.73m x 3.09m x 2.33m, ie about 15m^2 floor area, with about 18m^2 of interior wall area inside our exterior west/north walls. 7m^2 of that is the north wall, while the west wall has two 1.48m x 2.08m window openings ie ~6m^2.
Having pondered the effects of the unexpected bonus plastic membrane behind the plasterboard, I realise that it will form a vapour barrier. The usual rule of thumb as I understand it is to have such a barrier 1/3 of the way from the warm side to the cool side (thermally) so that the inside will generally be above the dew point to avoid condensation which might result in dampness, mould and rot. The existing membrane is now way way further out than that thermally, so to try to minimise vapour migrating towards it from the inside we will vapour-tape the edges of the aerogel around the door reveals, and try to find a vapour barrier primer paint coat, oil or latex based.
Having asked on the Green Building Forum to comment on this scheme, "Saint" pointed out there's foil between the plasterboard and the aerogel. That could serve nicely as the warm-side vapour barrier, so as long as we are careful to block routes past the foil, eg at the exposed aerogel at the window reveals and at areas of damage, most of the work is done.
However, since we didn't seal/tape at the front of the boards, though all the joints were at least partly filled with foam, there's a possible moisture route through the skim into the gap between boards, so an impermeable paint base coat still seems to be a good idea, else we might have to gouge out the plaster and reseal there worst case.
Again "Saint" came up trumps with Gyproc drywall topcoat: "Acts as a vapour check when 2 coats are applied." Could be just the thing...
2010/07/23: Skirting board and plaster coving has gone up, and socket wall boxes fitted.
We are going to use a vapour-check drywall primer over all the newly-plastered surfaces and over the coving, and use an oil-based paint on the foam-sealed skirting board, to minimise air and moisture movement out of the room.
Due to a misunderstanding, the first primer coat on was breathable/permeable, but two coats of Gyproc Drywall Sealer have gone on top to provide vapour control.
2010/07/28: After three days all the priming and painting was completed, including skirting and the previously-unpainted internal door.
2010/08/23: All the radiator pipework fitting and re-routing has been done (and our microbore pipework has been banished from downstairs!) and the plastic reveals for the windows have been put in. The curtain rails were put back up for us.
2010/08/25: Having not seen any leaks from the radiator pipework I briefly turned the central heating on and bled all the rads again; everything seems to be working fine.
2010/08/27: Last night Jean put the curtains back up and today we had most most of the finishing touches done such as caulking the wall penetrations for the radiator pipework. Short of a couple of tiny paint touch-ups, we're done!
For the various elements of the room, and ignoring ventilation losses, my end-July 2010 estimates for their effective U-values are:
As of July 2010 I can probably assume that the overall U-value (especially for the external walls/windows) is a little less than 1W/Km^2, with the windows dominating. Thus for 18m^2 of external surface and 300W (3+ people) in the room we could sustain a temperature difference above external of about 17K/17°C without heating, which given our normal daytime thermostat setting of ~18°C suggests that we shouldn't need to heat that room until the external temperature drops below freezing. Average daily temperatures in London are essentially never below 0°C, so in principle we will now be mainly OK even if the heating fails. Even in rather harsh January 2010 there were only 17 degree days below zero (and less than that in total in the few months around it). Clearly other parts of the house need heat too, if for no other reason than to protect pipes from freezing, etc.
We're getting reflective/thermal blackout blinds to hang behind our curtains, to help keep out unwanted sun (light and heat) on summer afternoons, and better retain heat in winter. We've tested the same make of blinds on another west-facing room, and it certainly helps keep the room cool in the summer afternoon/evening.
In general I should check for and remedy thermal bridges and air leakage. A particular potential area of trouble is the internal plasterboard/stud wall between the living room and the kitchen; is it ventilated to the outside, and if so should that be fixed or would doing so risk rot for example?
(Livingston was very helpful 2010/07/19 saying that a typical low-end thermal camera with a USB connection to extract images from it would cost somewhere round £300--£400 for a 3-day hire which could be over a weekend, which would probably cover me. Ashtead Technology had a 2-day minimum hire for a little over £100/day for similar, so getting hold of this equipment is not prohibitively expensive or difficult.)
The glazing also needs to be seen to in due course, as mentioned above.
If the room air-tightness improves enough I will consider including MHRV (Mechanical Heat-Recovery Ventilation), possibly in conjunction with the kitchen.
The new floor with 9mm SpaceTherm is 1C warmer than vinyl+ply+floorboards, 1-2C warmer than just floorboards. All in unheated rooms. I've re-installed radiators today so I'm looking forward to seeing what [difference] it makes in a heated room.
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