Cavity wall question

[Steveb21]

Hello all,

Property:

Corner plot detached bungalow (Dormer conversion around 1988).
7 Rooms downstairs
4 Rooms on the converted Dormer upstairs
Double side garage
Wooden subfloor.... of prob 10" ... not enough to crawl.

Issue:
External walls are very cold, leading to cold rooms!

Property has cavity wall... i was considering getting this filled with beads a few months ago but i have held off as i have read a fair few issues regarding damp.

I have been up to the loft area a few hours ago and just about stuck a camera the furthest i could get... and by judging on the recording it looks like the cavity walls are open from the top.

Questions:

I am assuming i am losing my room heat through my walls, up the cavity, into the loft and out into the big wild world.... is that right?
Is it ok to close the top of the cavity?
Will it have much effect on keeping the rooms a little more warmer?
The area is pretty difficult to reach due to it being the the furthest corner... would it be best to lift the roof tiles from outside and insulate that way? It would probably give me a better idea whats going on anyway.

Any advice would be much appreciated.

 

[Burnerman]

Cavity wall insulation will help you to some degree - its widely thought that bead fill is the most satisfactory. During installation its vital that the air bricks are allowed to do their job - ventilating the underfloor.....to allow this, a duct may be installed so the air passage isn't restricted by the beads.
Leave the cavity open at the top......have loads of loft insulation that covers the ceilings fully but doesn't fill the soffits or touch the underside of the roof tiles.
I'd only disturb the roof tiles if necessary to replace the underfelt or whatever - best left alone in my opinion.
If your internal walls are really cold, and you can ensure that they cannot become damp its possible to batten the walls, add slab insulation (I could only use 30mm stuff though) and then plasterboard plus skim.
John

 

[Steveb21]

Hi John, maybe i have read too many horror stories regarding cavity wall insulation that its put me off. As it appears the top of the cavity area is open.... would the beads not just pour out? I have around 20 airbricks around the property and did mention this to the surveyor who came out to report of the cavity insulation.

I have not long moved into the propery... first thing i did was clear it out, plaster walls and paint. If i had known i would have this cold issue i would have added installation to the internal walls.

 

[tony1851]

Be careful adding cavity insulation - some external-skin brickwork is not suitable for this.

 

[Steveb21]

Be careful adding cavity insulation - some external-skin brickwork is not suitable for this.

Care to explain further? are you talking about properties which are at a greater risk to rain penetration ?

 

[Burnerman]

In an ideal situation, the cavities would be left completely clear and ventilated.....this prevents any water penetration from one wall to another.
To allow cavity insulation to work without any dampness issues, the outer leaf needs to be as impervious to water as possible. My own house is constructed largely from Northumbrian sandstone which is noted for its porosity. To accommodate this, my house walls are well overhung, with large eaves. I have helped this as well I may by coating the stone with a waterseal compound which soaks into the stone and then repels driving rain.
The cavities were injected with a fibrous wool.....for sure, some escaped through the top of the open cavities and escaped into the loft but no problems there.
I have to say I consider the house to be warmer (there may be some psychology here) but I did ascertain that there was no restriction to air exchange beneath the suspended timber floor.....there has been no sign of penetrating damp anywhere.
The final call has to be with you, of course - but I'd maximise loft insulation, have quality double glazing and attend to draughts before considering cavity wall insulation.
One of my better moves was to fit insulation to the inside of the walls, as I mentioned......however there is some loss of space, naturally enough. This was done in an extension which was originally the connecting garage, and I was able to insulate below the (concrete) floor too.
John

 

[Doggit]

It's more than possible, that a dormer conversion in 1988 wouldn't have specified very much insulation, so a normal bungalow would have loft insulation to keep it warm, but your warmth is going up into the bedrooms, and then out through the dormer walls. But are all the air bricks in the walls, or under the floor. Any in the walls will be allowing cold air in to the void, and as the top of the void is open, it's then going up and over the ceiling in the dormers.

 

[^woody^]

Any cavity wall installer will assess the wall for suitability, will give a long insurance backed guarantee, will be responsible for negligence under common law, and will submit a building regs application under their approved installer scheme.

What more protection do you need?

But the perception of a cold room is purely subjective. Whether wall insulation is the answer, or if room heating is also an issue, or if there are improvements required elsewhere should be considered. Not just wall insulation in isolation.

 

[tony1851]

Care to explain further? are you talking about properties which are at a greater risk to rain penetration ?

In filling the cavity with insulation, you are effectively isolating the outer skin from radiant heat within the house. Also, you are preventing air movement within the cavity. Restriction of both these means that the outer skin will stay cooler and wetter for longer, particularly during winter. This can lead to frost damage of the bricks in the outer skin if they are not completely frost-resistant (eg with cheaper, slightly under-fired bricks in some older houses). It can be a particular problem on north-facing walls.
Your local Building Control dept. will probably have experience of which houses - if any - in your locality are not suitable for CWI.

 

[^woody^]

This can lead to frost damage of the bricks in the outer skin if they are not completely frost-resistant

Heat still escapes, and this will be enough to remove the risk of frost to the outer skin. There are a few other factors too.

The only risk of frost remains at ground level below DPC (where the floor is) as this part of the wall will be cooler as there is no heat to escape at this level, and the proximity of external ground adds to the cooling effect for frost to occur.

 

[Steveb21]

It's more than possible, that a dormer conversion in 1988 wouldn't have specified very much insulation, so a normal bungalow would have loft insulation to keep it warm, but your warmth is going up into the bedrooms, and then out through the dormer walls. But are all the air bricks in the walls, or under the floor. Any in the walls will be allowing cold air in to the void, and as the top of the void is open, it's then going up and over the ceiling in the dormers.

1988 - maybe even earlier will need to double check on the paper work.

There are around 20 airbricks around the property - under floor. I assume that air also gets into the cavity through this way? (as well as the subfloor)
There are 2 airbricks up at wall height - in 2 of the rooms. I have blocked these temporarly from the inside and put a closed vent cover on (monitoring condensation in room, has been OK so far). As the 'void' is still open.... shall i block these airbricks from outside?

The floors are also cold (8mm lamiante flooring with 5mm fibre installation boards). I was considering insullating from the subfloor however there is not sufficient crawl space so that idea is out the window, i dont fancy ripping up the floorboards. May lay another type of installation down - any recomendations for this?

Thanks for all who have provided input so far.

 

[tony1851]

Heat still escapes, and this will be enough to remove the risk of frost to the outer skin. There are a few other factors too.

Several council houses near us had CWI added years ago, and the external brickwork - which had been reasonable up to then - started breaking up and had to be replaced in large areas.

 

[Ian H]

Several council houses near us had CWI added years ago, and the external brickwork - which had been reasonable up to then - started breaking up and had to be replaced in large areas.

I think my house has that problem, the insulation looks to have been a liquid that expended to fill the cavity. The front and side walls are sound but the back one is terrible.

 

[Steveb21]

Several council houses near us had CWI added years ago, and the external brickwork - which had been reasonable up to then - started breaking up and had to be replaced in large areas.

Are you aware of what type of CWI it was? Beads appear to be the 'safe' option compared to the other types offered.

 

[^woody^]

Several council houses near us had CWI added years ago, and the external brickwork - which had been reasonable up to then - started breaking up and had to be replaced in large areas.

Any more details? Actual cause, timescales?