Insulation question: cavity wall + internal wall?

ilikecookies

Hello,

Wondering if anyone could provide any advice on insulation ...

The background is we have done the obvious measures - ie. loft insulation, cavity wall and double glazing. That said we are still keen to cut down the heating requirements as far as we can as we're on oil and the house still seems to lose heat rather more quickly than other properties we've lived in (I think aspect may have a fair bit to do with it but certainly some more draft proofing wouldn't go amiss).

As plan to redecorate each room over the coming years I was wondering about the feasibility of adding insulation internally to the externally-facing walls (ie. using the boards made by kingspan, knauf etc) to help reduce heat loss further.

Obviously there is a cost-benefit analysis to be done but just wondering if technically it's even advisable. For example, might it cause issues with moisture? Or can this be got around by adding a porous layer underneath the insulation?

Any advice very gratefully received

Smiley_Dan

IANAB (I Am Not A Builder).

You do need to deal with moisture and use a membrane to stop ingress to the cold face, sealed with tape. I advise you ask here: http://www.greenbuildingforum.co.uk/forum114/

IMO the best job is to add EWI, you also get the benefit of far better air tightness and your walls begin to act like giant heat stores. You also don't lose space. But very expensive... there are no grants to add EWI to cavity wall properties (as far as I know, let me know if there are!!!).

Robwiz

What you're suggesting can be done and if you search online you will find write-ups by enthusiasts who have. As Dan says, the risk is that with insulation on the inside wall the boundary the insulation and the inner leaf of the cavity wall is colder and any water vapour in the void could condense on the wall causing mould. The way to avoid this is to ensure a solid bead of sealant along every edge and to tape the joins. A diy-er is more likely to be fastidious about this than a contractor.

The Green Building Forum consensus of opinion is to not reduce the wall's U value below 0.5. That's the figure usually achieved with cavity wall insulation.

With internal insulation, if you're going to do it properly you need to insulate the walls in the void between upstairs floors and the ceiling below. Getting condensation around the ends of joists which may lead to rot is not something to take risks with.

With the level of insulation you have, it's likely that you will be losing as much heat through ventilation losses as through the fabric. Therefore being obsessive about sealing gaps around doors and windows and all penetrations through the walls, floor, ceiling will pay dividends – around pipes, cables, light switches, sockets. Also, if you have suspended floors, all the gaps between boards and along skirtings.

It may be worth investing in an infrared thermometer to identify cold spots. I did and thought it money well spent.

Smiley_Dan

Robwiz wrote: »

The Green Building Forum consensus of opinion is to not reduce the wall's U value below 0.5. That's the figure usually achieved with cavity wall insulation.

In what context? Plenty of U values far lower than that...

Robwiz

Of course there are. The context was the OP's situation – where cavity wall insulation is pumped into an older house the resulting U value is usually reduced to around 0.5.

Smiley_Dan

Oh, I see. Yeah, depends on the width of the cavity as per http://www.thegreenage.co.uk/getting-to-grips-with-u-values/

ilikecookies

Thanks all - great suggestions as ever and ideas/avenues for me to pursue this further! In particular ...

Smiley Dan - you're right that EWI would indeed be a neater/the most effective solution. I discounted it assuming the cost would just be too high but I should at least get a quote as no doubt doing it internally will be expensive and very time consuming to do it properly so would be interesting to compare the two. I think grants may be location/council-specific as I do know an elderly lady in my location who received some grant for this from our local council (but not the full cost).

Robwiz - good point RE drafts, etc. Identifying these is proving problematic so I am considering a professional heat loss survey. Can you tell me the make and model of infrared camera that you have used so I can do a bit of research on that?

Thanks both!

Smiley_Dan

Grants were location / benefits / existing wall construction dependent. See the constituent parts of the ECO scheme. There's also (or was also) the GDHIF but that has closed four new applications at this time.

Draught proofing always worth doing.

Robwiz

I used a Flir i7.

It's worth contact your local council's sustainability team to see if there are community energy saving projects in your area. You may be able to borrow a camera or tap into a voluntary group with equipment available.

A realistic option is the Black and Decker infrared thermometer which works quite well.

Smiley_Dan

If you don't have a community scheme, Jewson now hire out thermal imaging cameras: http://www.jewson.co.uk/tool-hire/surveying-equipment/surveying/

We do have a community scheme, unfortunately it still costs, and more expensive than Jewson!