Cavity Wall Insulation Queries

[Bovvered?]

I've just had a survey by a cavity wall insulation company, they're one of two approved companies under our local council's insulation grant scheme. I'm confused over a couple of things they've said hence this post.

I have a detached garage that is approx 4-5 feet away from one gable end, they say that with this space for a ladder they can't safely reach the roof apex and I'll have to pay extra for a scaffold platform. I asked how high they could go on a ladder with the space available and they said up to the gutter line. Not being an expert in this field I'm wondering why do they need to insulate above the gutter line anyway? Is there any reason why I need to have the wall cavity in the loft insulated? If I don't is there a risk of damp?

My next query is about our lounge which is 26 feet by 14 feet. It has a gas fire with a normal flue and the room is double glazed with a bay window at one end and patio doors at the other, the patio doors are fitted with a permanently open trickle vent. The surveyor has told me I'll need a 150mm square wall vent installed at extra cost. The reason given being that CO2 produced by the gas fire won't be able to permeate through the wall once the cavity is insulated. Is this correct (and why) or just an unnecessary 'extra'.

TIA

[ARWadsworth]

I can quote Phil L (cheers mate) on this as he answered the same question I asked earlier this year. His answer was

"All walls must be insulated to the top of the cavity, so the peaks on gables are always done, this is to prevent any water that may ingress from tracking across the top of the 'stopped' insulation - if the cavity is 100% filled, the water will simply make it's way down to the DPC naturally."

Could your gable peak be done from the inside to save on the scaffold costs? If it is just a loft then that should not be a problem, if it is a bedroom with plastered walls it could be a problem.

I have never heard of a permeable wall that was used as a vent for a gas appliance. I wonder if new this vent is required as the cavity wall insulation would block up an existing vent.

Adam

[Bovvered?]

Thanks, I can see that now, although I can't see how water would ingress in the first place unless I lost a ridge tile, and that isn't something you wouldn't notice. At least they want to do a 'proper job' which is a good thing

No it's just a loft space so it could be done from the inside, I suppose it will just depend if they're willing to do that and if they have a long enough hose to go through the house, up the stairs and across the loft to the wall. >

There's no other ventilation from outside to in, just the trickle vent?

[Phil L]

As Adam has already answered this, I don't need to, except to say that water naturally runs down the inside of the outer brickwork during rainstorms - you don't need a roof tile missing or any other damage, water gets through small holes in the mortar and in some cases, the bricks themselves to get into the cavity.

You don't pay for scaffold though - they are trying it on, simply tell them that they can do up to the gutter line as normal, then they can do the apex from inside the loft like all the other CWI installers

It /could/ be required, but certainly not at extra cost - this has to be included in the job.

I've done houses that have needed 20 - 30 vents[1] installing and there was no extra charges invovled to the customer.

[1] underfloor vents, through vents and suchlikes, very often there were 3 or 4 on each elevation, sometimes a lot more - this is included - it's like an electrician charging extra for cable clips or a plumber for fittings.

They sound like a cowboy outfit to me, complain to the council, then get in touch with your energy supplier to find out about their grants, but first visit this website to see if you can get a 100% grant:

[Anna Kettle]

Could the wall be a red herring and the actual problem is that the trickle vent is closeable whereas his rules demand a fixed open vent?

If your wall is made of modern materials it likely wont be breatheable anyway

Anna

[Bovvered?]

normal to finish the job from inside the loft, no scaffold required. Regarding the vent, apparently the council requires their insulation contractors to ensure that gas venting is up to the latest standard for any gas appliance over 7KW. As mine is 6KW that's another 50 quid I don't need to spend. They are also required to do a CO test before and after the work to make sure they haven't got insulation in the flue. Cheers to you and Adam for input.

[Bill]

Regarding the gas vent - my CWI installers suggested the same even though the fires didn't need vents when installed 2 or 3 years ago, I think it was £75 per vent. When I told the 'surveyor' I would take the fires out (they are hardly ever used as most of the heat goes up the chimney) he insisted that it had to be permanently blocked up, I couldn't just leave the opening as a decorative fireplace in case I later put the fire back ! Absolute rubbish. I never did get a proper answer from the Installers, the Council nor the people running the grant scheme on the validity of this requirement. From what I could find on the net there is no specific requirement when the fire is below a certain Kw rating, they are just covering themselves, if a vent is fitted there is no need for the gas safety checks afterwards. If you don't like the rule you need to find another installer.