cavity wall insulation

[TheAngryDog]

A topic I am sure has been done to death.

The house we are buying has no cwi or roof insulation. I am aware of grants being available but I suspect that we do not qualify.

Is cwi and roof insulation worth doing in a 40 year old house? And with no grant being available, what does it tend to cost for the walls to be done? I know it's dependent on house size, but ball park?

Are there any issues to take into consideration? We are looking at having new vented fascias and soffits installed as well.

Thanks.

[toastyhamster]

Had ours done a couple of years ago, the grant was available to anybody but it only covers a certain square footage, you have to top up for the rest, think I paid around 500 quid. Definite difference afterwards, soon get used to it but heating bills dropped and together with solar (don't get started!) our dual fuel bills are pretty low and I'm usually one of the first in the country to put the heating on and the last to turn it off.

[TheAngryDog]

Thanks for your reply.

The house we are buying in a 4 bed semi, a decent sized one but not huge. 500 quid I would be happy with.

All of the Grant info I have seen seems to rule us out though?

[8-P]

Did mine last year (large 30 year old house)

Odd mix of messages.

I couldnt get anyone to do the loft insulation, they all made excuses because its a complicated space and I ended up doing it myself - found some insulation on ebay "left over" from a build apparently either way, £200 cheaper than b and q, ask no more.

I was told cavity wall grants werent available, but then the last person to come round a few months later told be it was no problem and sure enough Dyson did the job about 2 weeks later and a good job too - mortar matched VERY well.

As Im a sad nuts I record my gas an elec useage. I was 20% down Feb on Feb but I couldnt tell you if this Feb was warmer than last year or not. But my house does hold onto the heat noticeably longer and generally feels less icey.

[S6PNJ]

Time to resurrect this topic! I'm in the process of having my 1932's house surveyed for CWI and have asked Dyson (and one other) to come and talk to me. From looking at their websites and the claims, they seem to emphasise that the blown bead solution (EPS) is 98% air and thus very efficient. Well, currently my cavities are 100% air (save for the scraps and rubbish in the bottom of them!) so why is EPS (98%) better than air (100%)? I need CWI (or a surveyors report saying not) in order to qualify for the RHI - that's why I'm (being forced) going down this route currently.

[8-P]

Dyson blew in a mix of pva and polystyrene types balls to mine last year

[Mr GrimNasty]

S6PNJ said:

Time to resurrect this topic! I'm in the process of having my 1932's house surveyed for CWI and have asked Dyson (and one other) to come and talk to me. From looking at their websites and the claims, they seem to emphasise that the blown bead solution (EPS) is 98% air and thus very efficient. Well, currently my cavities are 100% air (save for the scraps and rubbish in the bottom of them!) so why is EPS (98%) better than air (100%)? I need CWI (or a surveyors report saying not) in order to qualify for the RHI - that's why I'm (being forced) going down this route currently.

It's highly likely your masonry will be very porous to rain (this may not be obvious - indeed the cavity may be bone dry 99% of the time, but under certain weather conditions, wind direction, quantity, persistence of rain etc. the outer leaf will saturate and your cavities will become like a waterfall).

It's highly likely your cavities are neither wide nor consistent enough to meet building standard recommendations for CWI, they will also contain a lot of debris.

Your house has remained damp free (presumably) and has operated satisfactorily for nearly a century with high airflow in the cavity - as it was designed - now you are going to prevent any significant airflow at all.

All CWI (despite not being water absorbent) will cause bridging by capillary action at the very least, at worst it will divert some erstwhile harmless gusher straight onto the interior leaf.

Why even bother looking into CWI? If you want insulation go straight to the alternatives, nowhere near as cheap, but it won't condemn your house either!

[S6PNJ]

Mr GrimNasty said:

Why even bother looking into CWI? If you want insulation go straight to the alternatives, nowhere near as cheap, but it won't condemn your house either!

Thanks Mr Grim - I totally agree on all you posted, but unfortunately:

S6PNJ said:

I need CWI (or a surveyors report saying not) in order to qualify for the RHI

Looking at the FAQs for the RHI, specifically Q13, I need to meet one of a very short list of exceptions. I'm hoping that any survey will say our house is not suitable and hence we can then get the necessary derogation to not have CWI. Indeed, up until earlier this week when I looked at the RHI FAQs, we were intending to line the internal-external walls with PIR board/plasterboard in order to not have to install CWI, so we'd much rather do internal insulation but if the RHI says we need CWI or a letter from our mum, then those are the hoops I need to jump through.

[Sheepshanks]

S6PNJ said:

From looking at their websites and the claims, they seem to emphasise that the blown bead solution (EPS) is 98% air and thus very efficient. Well, currently my cavities are 100% air (save for the scraps and rubbish in the bottom of them!) so why is EPS (98%) better than air (100%)?

I might be due a whoosh parrot here, but it's because at the moment the air is moving around.

Our mid-60's house can't be done due to inconsistent cavities. Three times people have knocked on the door and insisted it could be done, only for their surveyor to knock it back.

An old builder told me it's fine if the house was designed for it, but it should never be retrofitted. Yet most neighbours, with identical houses, have had it done with no ill-effects. We spend a bit of time in the house immediately next door and that's noticeably cosier than ours.

[Dr Mike Oxgreen]

Sheepshanks said:

I might be due a whoosh parrot here, but it's because at the moment the air is moving around.

Exactly. It's the same reason why putting on a cardigan makes you warmer compared to having the open air directly next to your skin. A cardigan holds the air stationary, preventing it from transporting the heat away from your skin.

But if the cardigan gets wet, the water will transport heat much better than air, so you'll be worse off than if you were naked.

[trickywoo]

Insulating the loft is a no brainier but doing the cavities is worth more consideration. If the house or significant walls aren't exposed to the wind and it's expensive to do it might not be worth it.