Hi
Don't be surprised if you get some negative comments as there are many on here who think multifoil insulation is not all it is cracked up to be. If you have a spare day or two have a look at the mighty multifoil thread on here. I am afraid I am not qualified to give advise on your project but good luck with it. We did use multifoil on our barn conversion and have been pleased with the results. My unqualified take on multifoils is you have be obsessive about sealing all joints and perimeters and if done very well you can get good results for the thickness it takes up but it is not cheap stuff and if you have space to spare you will probably get more bang for your buck with more conventional insulation.

Others more experienced than me will help you with this project.
Beau

Guys.

Thanks for your response. I, too, have read many differing opinions on multi-foils. I guess that is one of the aspects that leaves a bit of a question mark in my mind. Aslo, I have heard how the insulating properties of PIR boards decrease quite quickly over time. I was thinkging of rock wool, or something that is pumped in, so that it completely fills all of the voids. I should add that the above specs are what my architect has specified.

Cheers

I am certain that you should read this discussion before you embark on spending money on foil insulation http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=125&page=27#Item_30

Although greater thicknesses of insulation do return lower savings, think about the influence of an 8% increase in gas costs and it aint going to go down. On economic grounds alone you could insulate to below U=0.1

Also if you were to spend on insulation you could design out the heating system saving on capital costs, replacement costs, repair and servicing costs and FUEL COSTS -- appealing?

<blockquote><cite>Posted By: tony</cite>I am certain that you should read this discussion before you embark on spending money on foil insulation<a href="http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=125&page=27#Item_30" rel="nofollow">http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=125&page=27#Item_30</a>

Although greater thicknesses of insulation do return lower savings, think about the influence of an 8% increase in gas costs and it aint going to go down. On economic grounds alone you could insulate to below U=0.1

Also if you were to spend on insulation you could design out the heating system saving on capital costs, replacement costs, repair and servicing costs and FUEL COSTS -- appealing?</blockquote>

If I am honest, I have resigned myself to the capital ex for the heating system (ASHP and UFH), possibly because I am old fashioned and cannot get my head around not having a heating system, even if it hardly used. However, what can I do to insulate down to those levels (Passive or <0.1) without the need for thicker walls (currently 140mm)? Many thanks.

Take a look at this system , might be of interest , good environmental credentials
http://www.natural-building.co.uk/systems/new-build/pavawall

Posted By: Diablo96The architect has stated thta it should be less than 3m3/hour/m2 and has secified a MVHR system. However, given that it is a 240sq.m bungalow, there is a lot of pipework and I am getting quotes in the region of £7K. This is making me think twice about it

Then that is about one and a half air changes an hour, so for every cubic metre of air in the house 552 m^3 or 660 kg it will need 0.183 kWh for every 1°C difference in temperature between inside and outside. Say you heat for 8 hours a day and the temp difference is 10 °C that will be 14.6 kWh or about £0.73 a day just on air losses.
If you heat for 200 days a year, that could be about £150 a year at 5p/kWh, half that with a COP of 2.
Now you need ventilation in a modern well built house (mine is pretty good and if I keep the windows closed it soon smells odd), so re think the need for MVHR and look for a better quote. You can also look at the Exhaust Air Heat Pump thread that was entertaining.
As for ASHP, if you are near the coast think twice about it, even 2 miles in land here can cause corrosion problems, and most of the ones I notice are rattling. They seem ideal for people to lean a bike against.

Look at Viking House 'timber frame warm stud', Seamus is also quite active on here. Also look at all post on here from Viking and fostertom, they have talked a lot about this. We were going to do almost the same as you and decided against, 140 studs are fine you don't need any thicker, foil breather may or may not be worth it ( still not sure myself), warmcell insulation?, for thicker insulation either external over sheathing with EPS or 'floating' extra studs internally. Be obsessive about insulation and airtightness, esp with mvhr

Oh, and welcome. Where are you, tell us more about what you want to achieve?

It is your decision in the end, PUR vs EPS, multi foil or not, heating system or not. but you have posted the question asking for advise, and what you are getting is good educated advise from a community that has been discussing these issues for years, my advice would be take the advice your given, seriously think about your about your build and budget before you start, it’s never too late to jump ship.

It's all a numbers game! Even if you go to full passive spec you are still going to require something like 10-15W/m2/a so for 240m2 2500-3600kWhr/a for space heating and another 3,000-4,000kWhr/a for DHW.

It's a question then how you are going to meet that demand?

Depending on your choice you will then know how much an additional 4,000-5,000kWhr/a of space heating is going to cost you. You can then decide if it is worth your while going passive or not.

We are presently building a similar size house, we have started with a 145mm frame insulated with Paroc mineral wool then another layer of 145mm mineral wool is added inside then a 70mm stud wall for services which is also insulated with mineral wool. That gets us down to a U value just below 0.1 but we also lose about 15m2 of floor space compared to if we just went with 145mm walls.

We will (probably) install a 5kW Ecodan ASHP for the DHW and space heating demand.

On purely financial grounds the extra insulation is at best marginal but we can relax and never have to worry what energy prices are going to do in the future and that for me makes it worthwhile.

Indeed we might all have cold fusion reactors under the kitchen sink in 5 years time and all those low energy investments will look pretty silly, but I guess I have placed my bet!

Posted By: CerisyWe have just started the groundworks for our timber framed house - at last!

The wall make up is: T&G cladding (hopefully thermowood) on 25 x 50 battens on breathable membrane on 38 x 89 sw timbers laid horizontally with 75 thick semi-rigid insulation between. Then the frame from TTF in Hull - 9mm OSB on 38 x 140 frame fully filled with Rockwool flexi, then 100 thick semi-rigid insulation, then 38 x 89 internal wall filled with 75 thick insulation, then vapour barrier sealed as the air-tightness layer, then 25 x 50 battens to form the services void and then plasterboard. Loads of insulation!

Fitting MVHR and, eventually, a room sealed wood burning stove for back-up when EDF decide to cut the power - well, it is rural France - and as eye candy for my better half!

Frame is planned for 20 November - now to get the foundations laid ...

Sounds good, I'm jealous, what's your target u value and what's the roof construction as well as rest of plans

No - it just took the first floor - ground floor attached!!