covering/blocking Air bricks

[Chris]

I am in the precess of building some decking in our back garden that runs the width of the house. Along the wall of the house is a series of air bricks.

The final height of the deck boards will be above these airbricks, but they will remain unblocked and uncovered in the void beneath the deck boards, and there is enough room below the beck boards and joists etc to get a good airflow.

On this basis, I'm not too worried that the airbricks are below the deck board level, but my wife is convinced that they will then be as good as covered, and that we'll get damp, the house will fall down and the universe will come to an end.

Does anyone have an opinion on this??

Thanks

Chris

[Chris]

Okay, as a follow up, the concern is now also that the deck is above the dampcourse. these folk say it is okay, so long as there is a gap, and I plan to make it about an 25mm

my airbrocks are below the damp course, it implies that it is not a problem. Are all airbricks below the DPC? If they are to keep the subfloor void ventialted, I dont see how there can be airbricks below the dampcourse...

Thanks Chris

[The Medway Handyman]

Assuming the wall plate or joists don't block them, I can't see it being a problem, you also have the gaps between the deck boards to allow air flow.

Eventually of course, the house will fall down and the universe will come to an end, but I don't think either will be caused by your decking!

[Guy King]

The message from "Chris" contains these words:

Can't see a problem /except/ that when they're beneath the decking you won't be able to easily see them to ensure they stay clear.

[Andrew Mawson]

For the sake of marital harmony you could knock out the airbricks, cement in a 100mm brown plastic soil pipe, and extend it to the far side of the decking where you terminate it in another air brick. There is absolutely no need to do this other than to keep 'her indoors' happy !

When I built my attached garage I used this technique, but then it was through a solid concrete raft rather than a draughty bit of decking. The BCO was most impressed

AWEM

[meow2222]

If theyre below the decking, air movement at the brick will be reduced, air exchange through the airbrick will go down, and RH under the floor will rise. This is not a good idea imho. You may well get away with it, or you may not. Also the air under the decking may be of higher RH than in freer air, depending on the rate of air exchange between under deck and the wide outdoors..

Just leave a space between decking and airbrick, and all is solved.

I dont suggest using a long pipe from airbrick, as this will greatly reduce the exchange of air between underfloor and the outdoors.

Bear in mind the uiverse could end if the house gets damp and rot, the insurance refuses to pay, and she decides youre a total pillock and never forgives you. Unlikely I know, but one of those risks not worth it.

PS there is usually no dpc in suspended wood floor houses. It is mportant to keep exterior ground levels well below interior floor level. If I were you I'd leave a gap between deck and wall all along, and maybe cover it for safety with some kind of open mesh.

NT

[Phil L]

Incorrect, almost all suspended floored houses have a DPC, some even have two, one below the airbricks and one above, almost all of them have at least one

[Andrew Gabriel]

That's not enough to avoid splashback up the wall. If it's a cavity wall, that probably doesn't matter. If it's a solid wall, I would be a little more concerned.

[Phil L]

Where else are they going to be? it's no good having them above the DPC or they would be visible above the skirting board inside, not much use for getting fresh air underneath the joists.....the DPC is the same level as your floorboards BTW.

as far as your main post goes, ignore the wife, so long as there is a gap between any joists and the vents, they will do the job they were intended to do, IE allow air in, it doesn't have to be a gale force wind.

[<me9]

Mine are below the joists. Building regs require them below the woodwork. You'd get rot otherwise.

[Phil L]

Correct, they are also below the DPC.

[Gav]

have you considered the effects blocking the vents may have on any gas appliances, if you are steadily blocking up 'draft' sources these may also be doubling as air vents to aid gas appliances. just a thought!

i would have a spillage check done at least if you are blocking vents up

[meow2222]

not so. I cant think of any reference to offer you though.

NT

[Donwill]

Have you considered using telescopic vents to connect the air brick to the air above the deck, so to speak, they are in the screwfix Cat 81 on page

497. 12025-81. At only £2 ea they may be worth the investment. Cheers Don

[Chris Bacon]

The vast majority do have a DPC, for some reason some have air-bricks, originally grilles, under the DPC as well as over it. You sometimes can't *see* the DPC, because it is buried, but it's there. PL's right.

[Andrew Mawson]

air-bricks,

right.

I suspect that in most cases where the airbrick is over the DPC they are using one of those cranked ducts shaped like a periscope so that the actual ventilation on the inside is below the suspended timber floor.

AWEM

[Chris Bacon]

Sorry, I had in mind older houses, should have said.

[meow2222]

please get a clue

[Phil L]

How many have you actually changed / seen / worked on?

Here's a clue for you: I worked as a cavity wall insulation installer for ten years, we typically installed insulation in 2 - 3 houses per day. The vast majority of these had underloor vents and they almost always filled with insulation, mening that they had to be smashed out, sleeved and new airbricks fitted, most houses had at least 9 underfloor vents...all this means that I have changed at least 22,000 underfloor vents in my time. You may have noticed one or two houses without a DPC, this is certainly not the norm, suspended floor or otherwise.

[meow2222]

Sonuds like you've seen a lot of houses. But one thing puzzles me: you say the vast majority had underfloor vents, yet of the buildings I've seen (a lot less than 2000) nearly all the modern ones have had concrete floors, not suspended timber. Since a poured concrete floor is cheaper, I would expect it to be that way. And concrete doesnt need underfloor vents.

Of the pre-1900 buildings, where suspended timber is the usual floor type, most have had no dpc, though I accept I've not seen 2000 of them.

NT