Hi,

Been lurking and reading for a while, very helpful, thank you one and all.

My wife and I, plus two teenage kids away at school/uni term time live in a large house (2 floors, ground area 300m2); I work from home and another 4 or 5 people join me during the day.

House was built in early 60's. Concrete floor, block-and-beam first floor and flat roof, now with insulation above (too thin I suspect) and pitched roof added.

Only South facing window is the one at the end of the upstairs corridor - overlooking garage

Central heating is cast iron skirting rads. Whole house is a single zone (although: one "out" pipe and two returns, we've put motorised valve on one of the returns but that has, sadly, only isolated rads in 1.5 bedrooms)

A pair (one for pool) of oil boilers now replaced with batch log boiler and 5 tonnes of hot water spread over two accumulators, also heated by Solar Thermal (6 large panels, South facing) in summer. From that heat exchangers for central heating (in position of original boiler, original unpressurised plumbing remains on CH side), DHW via low pre-heat and high coils in accumulator (i.e. mains pressure, and improvement over previous gravity), and another heat exchanger where the pool's heater used to be.

Retro fitting good insulation and UFH looks miserable - financial and upheaval.

We would like a large farmhouse-style kitchen, current footprint doesn't lend itself to achieving that.

So plan is to replace garage with 65m2-ish two-storey extension which will be due-South facing; kitchen / snug / living downstairs, master bedroom etc. above. Super insulate that and hibernate there in the winter. We can open, and heat, the State Apartments in the main house for highdays and holidays during the Winter, but as I hate entertaining in the Winter it won't be often I am hoping that rest of the Winter we can set the main house thermostat back to, say, 15C??

I am sure to have loads of questions in accomplishing that build.

Before the new build I'm still looking at improvements to main house. Originally built with Crittall metal windows, replaced (by previous owner) about 15 years ago with uPVC double glazed (probably around the time the pitched roof was added). We had cavity filled about 5 years ago.

Condensation on occupied bedrooms, and kitchen, windows on cold winter nights is significant (wiped each morning with sponge and wrung out to basin). Memory not good enough to be sure, but I suspect this is [worse] since cavity fill. We have some black mould that grows on the seals, don't remember seeing that before cavity fill. We have dehumidifer that we move around the rooms in late Autumn - makes the house feel a lot more comfortable - but by mid November it doesn't extract much water - so probably not doing anything useful?

Is there some sort of MHVR I can retro fit? I read about air tightness being crucial, and I doubt we have that (but is there a rule of thumb I can use to know if it is good, bad or indifferent?)

Would it be essential to duct to the ground floor as well? (Easy enough to use the loft space, harder to hide pipework to the ground floor; there are a couple of fitted wardrobes that would do, not enough for every downstairs room though)

Many thanks.

Good points.

The South end of the house is currently the garage. Significant issue for us is that there is a nice view to the South, we currently have no Southerly solar gain, and we would like a large kitchen / living space, so we had always planned to make the garage into that space. Thus the intention to do this existed before we realised that insulating it well, and living in it (i.e. relocating master bedroom to also be in the new extension, and have the benefit of the views) would give us a comfortable, and cost effective, living space for the winter.

Only reason for, subsequently, heating the main part of the house in the Winter is that my colleagues come in to work. They are in a couple of rooms that can be heated independently, but they wander to the loo, kitchen for a cuppa etc, but my "15C" was intended to be whatever temperature would not disrupt the building, and wouldn't be too cold for the inhabitants.

Would dropping the temperature to frost-free all winter have no impact on carpets and fittings?

We would like to replace the windows - the house would benefit from something that had less chunky appearance than the uPVC. I had assumed it would be very expensive and wasteful to replace windows that seems to me to be "quite young" - will we be thinking that today's windows are "rubbish" in 10 years time?

Definitely worth investigating though, thanks for the pointer. I wonder if an alternative is to consider some sort of insulation for the existing windows? Perhaps some [thermal] shutters that could be closed semi-permanently in rooms rarely used in winter, and at night in the other rooms? Perhaps more eco-friendly than physically replacing the windows?

Thanks DJH.

We had folding shutters in a previous (Georgian) house. With just one hinge (on each window-half) they parked in the reveal, so I guess the reveal must have been at 45 degrees.

Half the width of my window is 60cm, and the reveal is 17cm

Maybe they could open against the reveal and then hinge at 17cm and the remaining 43cm park along the wall - behind the curtain. Bit of a PITA holding the curtain away each time.

Maybe changing the reveal to be at 45 degrees and create a casing (is that the right word?) for the shutter is doable for DIY? I quite fancy spending the winter evenings making shutters for all the windows :)

I think lift-out and hang-on-wall is a bit of a nuisance, and likely to get biffed.

Many years ago I went on a guided tour of Wellington's house at the end of Park Lane. In the Salon, upstairs, there were floor to [high] ceiling windows. The guide first closed the conventional shutters and then a mirror, the height and shape of the window recess, pulled out of the casement and rolled across the window; it must have made the room look fantastic at night! I have no idea what that sort of intrusion into a modern [normally filled] cavity would do? Not easy to retrofit I suppose, but something I would like to consider for the new extension.

Presumably I need to make something air-tight otherwise there will be condensation issues behind a closed shutter?

And ideally backed with Kingspan or somesuch?

Maybe I should just spray some water on the windows and press some offcuts of bubblewrap on for the winter ...

Posted By: SteamyTeamaybe Aerogel backed ply and a skim of plaster, can be done room by room and if done right can improve the airtightness.

I'd appreciate if someone can explain airtightness to me, or point me at a description.

I understand that air can flow under my front door, and perhaps my uPVC windows don't fit tightly (but I can't feel a draught). But I think this also relates to air moving "though" the walls? If so I'm stuck on understanding that one.

Which brings me onto the MVHR. Without a sealed house it is probably pointless.

Thought that might be the case.

Get the loft sorted this weekend, doing mine, which was not too bad anyway, halved my heat load.

OK. No doubt I should have done it years ago. When they put the pitched roof on (over the original flat roof) they just left a hatch in the outside of the roof; no access from indoors. Its a pain to get a ladder up, unscrew the cover, and get inside. Upside is that its just a single clear space inside, no water tanks, wires, etc. so I can just lay more on top of the existing.

What depth should I be aiming for? I'm comfortable with spending a "reasonable" amount of over-spec.

I just add more on top? or does there come a point where the underside of the roof needs insulating, instead of more on top of the "ceiling"?

On the subject of heat load, do you know how much your place currently uses?

How would I measure that? We are burning logs now. I can find out how much oil we used to burn, before logs. Bit muddied by the fact that some oil would have heated the pool, but I may be able to guestimate Winter/Summer usage. Ah! I have measurements of "height of oil in tank" from back in those days, which I think I converted to Litres of oil / day. Dunno efficiency of the old boiler, but it was old and knackered - would that be any use?

I'm near Bury St Edmunds, Suffolk

I feel badly just asking questions ... if anyone needs any advice on gardening I may be able to reciprocate.

Posted By: SteamyTea

Posted By: KrispyI'd appreciate if someone can explain airtightness to me, or point me at a description.

Airthightness is really about blocking off holes. What is often forgotten about is the void between floors and where it interfaces with the wall, and where any pipework exits the building.

I'll read the link, thanks. Your description above may mean I am better off than most?

We have concrete floor downstairs, block & beam 1st floor and also for the original flat roof. All pipes are sealed into the floor (screed, or more). We do have [lowered] false ceiling under one bathroom, for pipework, but in floor above its all sealed back in again. Upstairs ceiling has no cables/pipes passing through (and no recessed lights). All wiring is "mineral wiring" [if I have the right term] and buried in the plaster, so nothing trailing in loft!!

There is no external pipework. All foul pipes are in vertical ducts within the building - discretely built into corners of rooms.

Might that mean that I could consider MHVR? I'd have to sort the wooden front door for sure (its not bad, and you come through a second, inner, door to get into the house - dunno what that's called - Vestibule perhaps?). The other external doors are uPVC and hopefully relatively tight fitting.

Posted By: KrispyI just add more on top? or does there come a point where the underside of the roof needs insulating, instead of more on top of the "ceiling"?

In this situation it makes no difference, pile it on top.

OK. Leads to my next question. I've only been into the "loft" once (accessed from roof, so needs ladder), so my memory a bit hazy. My recollection was a sea of pink insulation. Any tips on how to get around up there to lay more on top? Presumably I should not be trampling on existing insulation and compressing it?

Posted By: KrispyHow would I measure that? We are burning logs now.

Oil is about 10 kWh/litre.

Last complete winter figures I have is 2007/8. Looks like didn't started using boiler until beginning of November (which sounds about right for average Autumn). Figures based on weekly measurement of height-of-oil-in-tank

Nov '07 16-20 L/day
Dec '07 20-24 L/day
Jan '08 20-28 L/day
Feb '08 16-28 L/day
Mar '09 14-16 L/day

Not sure when stopped as final central heating use occurs at same time as initial heating of the pool (so might have been end-March, or some time in April)

The boiler was used also for DHW. Taking a period mid-summer when we would not have needed to heat the pool (before ST installed) looks consistent at 4 L/day to heat DHW (towel rails used to pull DHW around the gravity circuit, so maybe most of that energy was space heating, per se. Much smarter systems in place now.)

Average 20.48 L/day over 147 days (inc 4L for DHW). Oil Boiler was rated 70kW and ran for about 4 hours a day (which is a bit adrift if I should be doing 20.48 L per day x 10 kWh per Litre / 70 kW which would give me 2.93 hours burn which I think is too short, even worse taking off 4L for DHW. But maybe 4 hours burn would not be at full fuel rate ... just looking to see if sanity-check looks OK)

(Footprint is 300m2, 2 storey)

Posted By: SteamyTeaHave you thought of PV?

In a way.

Would have liked to help myself to FITs. South flat garage roof already taken up with ST. Did not want to move PV after (and onto) extension once built. Certainly did not want to store it for a year during build. So decided to wait.

Extension will include replacing the uPVC pool enclosure with a "building" of some sort (there is a tricky cost equation for us on that one!) but the uPVC is utilitarian/ugly, probably nearing the end of its life, and would be a major annoyance if snow-load or high-wind destroyed it.

Design for replacement has double-ridge roof East-West, so the more Northerly ridge could have PV on the South facing slope (i.e. invisible from ground level). Need to allow for the shadow cast from the more Southerly ridge in winter.

Pool enclosure footprint is 25M E-W and 12M N-S - so in principal could have a 25M run of PV panels. I would quite like to put the ST there too ... but its some distance from the Accumulator, so may put ST on the South facing roof of the extension for more direct/shorter route to Accumulator.