Cavity wall insulation

[tripty]

Hi,

I had British Gas round yesterday to see if we could get cavity wall insulation, the house is a 4 bedroom detached built in 1988.

The BG guy said yes we are eligible for *free* cavity wall insulation but they could only do 3 walls because one gable end is less than 1.3m from the next door neighbour and is too high for ladders, the ground being ~1.5m lower on that side. He said they'd have to use scaffolding if they did do it which is £400, fixed price from BG, and not covered by the governments grant.

Now, after he'd gone I was thinking couldn't they do the fourth wall from the inside? Having searched online I have found one forum post saying it can be done from the inside. I'll have to ask BG on Monday if they're prepared to do it.

However, being a bit inpatient I was wondering if any of you nice people could help:

- Is it possible?

- Approximately, how many holes would need to be drilled from the inside for the one wall, the wall is a gable end with one window and one air brick. BG said the insulation would be glass wool.

- Could all the holes be drilled in the attic?

Thanks.

 

[stuart45]

- Is it possible?
Yes

- Approximately, how many holes would need to be drilled from the inside for the one wall, the wall is a gable end with one window and one air brick. BG said the insulation would be glass wool.
There are set patterns which you may find on the net.

- Could all the holes be drilled in the attic?
No

Thanks.

 

[Nige F]

1988 I thought they were using cavity Batts when new build then. Where is Noseall

 

[stuart45]

Thet were on some houses, but you could meet the U values by using 5 inch aac blocks. I think they went from 1.0 to 0.6 around 82 until 0.45 in the mid 90's.

 

[tripty]

1988 I thought they were using cavity Batts when new build then. Where is Noseall

Ermmmm crap national builder, Ideal Homes if anybody remembers them Having said that the inner leaf of the house is thermal block, the original builders did say that it wouldn't ever need cavity wall insulation ever because of this - didn't really believe them though. Do you think there is much point adding cavity wall insulation?? The house gets very cold downstairs though, all windows & doors have been replaced with upvc.

I did a bit more digging, after your replies, and discovered this:

http://www.knaufinsulation.co.uk/pd...Insulation Supafil Cavity Wall Insulation.pdf

Its shows the pattern on page 6, I see why drilling on the inside isn't such a good idea.

 

[ajrobb]

Having said that the inner leaf of the house is thermal block

You are unlikely to see a return on £400. Assuming 100mm Thermalite blocks for the inner leaf, my dodgy calcs show your current walls might have a U-value of just over 0.7:

Untitled

• ajrobb
• 21 Mar 2010
• 1

This is already as good as 1930's cavity walls with CWI. Add CWI to your walls and the U-value drops by just 0.3:

Untitled

• ajrobb
• 21 Mar 2010
• 1

This is not much of a saving compared to a 1930's house, which would see an improvement of over 1.0.

I'd look for other reasons for downstairs being cold. Have you tried heating it?

Not all uPVC windows have grade A insulation.

 

[Nige F]

Interesting- Also, with a C-rap national builder the rads could well be under sized even allowing for uPVC windows . It`s looking like rads and maybe max out the roof insulation

 

[tripty]

Thats very interesting, cheers for the calcs and ideas. The problem with the house is that its cold downstairs but hot upstairs, obviously hot air rises so this is not something that can be easily eliminated....

Loft insulation is 110mm at the moment, was wondering about increasing that to 270mm+ but the problem is around half the area is boarded or has spotlights through the ceiling. So didn't think any extra insulation would do much.

Maybe I should forget insulation and concentrate on getting a new boiler and bigger rads.

Thanks again.

 

[ajrobb]

Yup, tot up the radiators and see if they come close to loading the boiler - pop a post into Plumbing forum. (I'd fit oversize radiators with thermostatic valves in the lounge 'cos I like that area to warm up first.)

 

[Nige F]

Thermo rad valve all round . Don`t rush out and get a new boiler though Post as much info on your system as you can on the Plumbing forum

 

[noseall]

Post as much info on your system as you can on the Plumbing forum

........so that they can argue for days and confuse you completely!

 

[tripty]

........so that they can argue for days and confuse you completely!

Thanks very much guys for your help.

I'm applying to the warmfront scheme so I'll have to see what they say. Would prefer them to do the boiler rather than insulation as it'll be the biggest cost, save most money and most environmentally sound to go from a G rated to A rated boiler.

 

[bosyuk]

This is really interesting, when we moved in the energy report said we had cavity wall insulation but the walls upstairs seem colder to the touch.

Its almost like they couldn't be bothered to insulate the higher parts of the building but if they couldn't get to them because of not being able to get a ladder that high because of the neighbours house and the hill that could explain a lot!

Will have to investigate!

 

[mointainwalker]

Energy reports tick what should have happened at the time per regs ( there is no physical checking of walls ), however from reading posts ( and I am not certain about this ) even 20 years ago builders were allowed alternatives to meet specs, so even though the report says "cavity-wall insulation " , your builder might have chosen to use thermal blocks to meet the spec and so the void could still be.......................void !