Renovating 1948 terrace

[Quakered]

Probably stating the obvious but from an insulation perspective, the only walls that matter are the external (front and back) of the terrace. As long as the neighbouring houses are inhabited (and heated) the loss to these can be ignored surely. The neighbours might even like there house hotter than you do and will therefore provide you with some heat for free.

The best place to measure the wall depth is via an open window in the front and back. If you are getting a full structural survey, you could ask the surveyor to provide the information.

[pdf27]

OK, finally got the structural survey done. Turns out that the front and rear walls are filled cavity, and the solid wall is only on the ground floor where a passageway goes through the terrace from front to back. Except for the kitchen, the ground floor is suspended wood.

Current latest and greatest (!) plan is:
- Solid wall insulation along the wall facing this passageway
- Underfloor insulation
- New gas condensing boiler
- Multi-coil thermal store (~250 litres or so)
- Wood burning stove - toying with the idea of getting a Dunsley Yorkshire and plumbing it into the central heating and hot water system, but a bit put off by the extra cost.

All this would be done right away before I move in, along with a few other updates (new kitchen, bathroom, etc.). Total available budget is 20k, so I'm pretty confident I can get all this done at once.

Long term additions/now if the budget is there:
Solar hot water - East/West facing roof, so not ideal, but the hot water system will be set up to take it.
New windows - current ones are OK, but showing their age a bit.

Finally, having been looking at all sorts of renovation things recently I've seen a lot of MVHR systems - I'm struggling to see how this could actually work in a refit rather than a new build, but since the energy savings are potentially massive then I figure if it's possible I ought to consider it. Anyone tried it?

[wookey]

A lot more MVHR experience over on the green building and AECB forums. They don't save 'massive' amounts of energy in themselves - it's insulation and airtightness that does that, and a corollary of sufficient airtightness is MVHR. It does require a lot of work to make an existing house aritight enough to fit an MVHR but it's perfectly doable. I'm working on it here. If I were you I'd not rely on the cavity wall isulation and add some more internally or externally and (if doing it internally) use that to form the airtight layer, connected to the underfloor and loft insulation. You will need to treat the party walls for airtightness to - plenty of holes through to next door in most terraces.

[pdf27]

Not so convinced about the insulation - a quick back-of-an-envelope calculation says that going from U=0.6 to U=0.3 on the outside walls will only save about 10% or so on the heat demand - with about half the heat demand being needed to warm up the ventilation air.

[Quakered]

one inch of insulation on the outside of a 9 inch solid wall should reduce the heat loss to 25% rather than the 50% you are assuming surely?

[dhaslam]

When you save 10%  of the heat  requirement you save it from the gross figure.    In practice something like 50% of the heat requirement can come form  passive heat, cooking, TV  lights etc., so you  could be taking a fifth off the actual  heating requirement.    Also there is  improved comfort  in having warmer walls.    

If you have a  good south facing position in the garden it might be better to place your solar panels there.   Also  in the longer term you should  try to get as much of your heat requirement as possible from solar.   For solar winter heating the panels have to be at the optimum angle.   In January I was getting  half of the daily solar gain  I am getting in August and the difference  would be a less if the panels weren't mounted at a fixed 35 degree vertical angle.

[wookey]

Not so convinced about the insulation - a quick back-of-an-envelope calculation says that going from U=0.6 to U=0.3 on the outside walls will only save about 10% or so on the heat demand - with about half the heat demand being needed to warm up the ventilation air.

Even if that was right, and I can't erasily check if you don't post more details, but simple block U-values like this are not really very accurate. In practice cavity insulation is often much worse than the simple sums would suggest due to rubble in the bottom of the cavity and imperfect blowing leaving gaps. Then there is the effect of thermal bridges. Internal (or external) insulation removes many thermal bridges and massively improves airtightness so the effective improvement you'll get should be much better than the simple 0.6-0.3 comparison. (and if doing this I'd go for 100mm for PUR rather than 50 giving you U<=0.2 as the insulation thickness cost is trivial in comparison to the work involved).

It is true that as you get to decent insulation levels like 0.3, 0.2, 0.15 ventilation heating starts to dominate, which is why MVHR makes so much sense.

[pdf27]

Sorry for the intermittent posts on here, I seem to have the worlds dumbest lawyers so am concentrating on getting the house right now!

Wookey, the assumption I'm making is that the outside walls are a poorly/thin filled cavity, giving a U~0.6. The house is ~8m wide, ~5m high giving a surface area of ~80m2. Floor/ceiling areas are about the same as the house is ~5m deep, giving a volume of ~200 m3.

For a given temperature difference, say 24°C between inside and outside, and one air change per hour this gives:

Walls: 80 * 0.6 * 24 = 1.15 kW

Air: 200 * 1010 * 1.2 * 24 / 3600 = 1.62 kW

In other words, dry lining the cavity wall to meet current building regs will only save 500W on a very cold day, and even taking it down to U~0.2 will only save about 800W. Blocking up the whacking great holes in two of the walls (to feed air for the gas room heaters) will have a much bigger effect, for much lower hassle and outlay.

[dhaslam]

If you look at the figure after insulation  to say a u-value of .2  you get to a figure of  .38 kw  through the walls.  With the same loss  again twice through floor and ceiling  the heat losses through the house structure would be 1kW maximum. With reasonable (net) loss through doors and windows  plus ventilation the total heat requirement would be tiny and at that level I wouldn't bother with either the gas boiler or the  boiler stove, just a very small woodstove.           

[Paulh_Boats]

Probably stating the obvious but from an insulation perspective, the only walls that matter are the external (front and back) of the terrace. As long as the neighbouring houses are inhabited (and heated) the loss to these can be ignored surely. The neighbours might even like there house hotter than you do and will therefore provide you with some heat for free.

I can confirm that. My late Father's 1932 end terrace was empty last winter - the living room was usually around 9C, it dipped to 6C in the exceptionally cold January 2010 weather. All that heat came from the neighbour!

-Paul

[pdf27]

With reasonable (net) loss through doors and windows  plus ventilation the total heat requirement would be tiny and at that level I wouldn't bother with either the gas boiler or the  boiler stove, just a very small woodstove.

Gas boiler will be required to make this easy to sell in the long run, and provide low level heating if I'm away a lot in winter (my fiancée's family live in the US). The existing one is ancient and needs to be moved anyway, so replacing it makes sense.
As for the boiler stove, still thinking about that one. Having looked at the numbers again, I agree I only need a small stove (<5kW). I'm still tempted to go with one with a small boiler though, to enable me to have hot water in the case of extended power cuts, or if the gas supply goes out. That is a serious risk in the 2015-2020 timeframe - to keep the power on requires a whole load of gas-fired power stations that haven't been built yet. If they don't get built, or if the Russians start getting shirty and there is also a problem with the LNG terminals, then we have a major issue. Spending a bit more to guarantee hot water availability is tempting.

[Loir]

I would second (or third) the MVHR idea.
Double glazing, draft proofing and solid walls may lead to condensation problems without sufficient ventilation.
And I hate the idea of just blowing heat out of the house.

Fitting an MVHR system is a lot easier while you are doing everything else. Getting ducting into the right places can be a pain as an afterthought.

I fitted ours about 15 years ago (a Wickes kit no longer sold) and it's brilliant. 

Loir

[dhaslam]

Some ways to  have automatically controlled heating are   heating coil in the  heat recovery system, electric underfloor heating and or thermostatic heated towel rail  in bathroom.    Electricity  from renewable source, of course, and  timed to  heat mainly in off peak hours when it is coldest anyway.         
 

[pdf27]

Electricity  from renewable source, of course, and  timed to  heat mainly in off peak hours when it is coldest anyway.

Unfortunately, right now renewable supply is fixed - so any decision I make to heat with electricity will be made up by the load-following (peaking) plant - right now that's coal fired. Electric resistive heating running off a coal-fired power station is only a little more efficient than burning the coal in an open fire! Renewable electricity tariffs are a good idea - they subsidise the increase in number of renewable generating sources - but many people are treating them like the medieval concept of indulgences. You know, "pay all this money to us and your carbon sins will be forgiven".

Heat pumps are somewhat better, but even then you have the issue that I would be adding an electrical load to the grid, which is made in the margin by coal fired power stations. Given transmission losses, etc. then with gas-fired electricity a heat pump needs a COP of about 2 to beat a gas boiler in CO₂ emission terms. Change this to coal-fired electricity and this then needs a COP in excess of 6 - and I'm not aware of anyone doing this yet. Where mains gas is available, heat pumps just don't make sense - at least until the marginal production of electricity uses a lower-carbon form of electricity than the current coal plants.

[pdf27]

I would second (or third) the MVHR idea.
Double glazing, draft proofing and solid walls may lead to condensation problems without sufficient ventilation.
And I hate the idea of just blowing heat out of the house.

How far did you go in making your house airtight before you fitted it? Have you ever tried running with it turned off for a few days in winter to see what difference it makes to the feel of the house? I'm somewhat concerned as to how airtight I need to make the house before I'd notice any difference.