Cavity wall insulation, airbricks etc

[Swampie]

I've been thinking about cavity wall insulation for our 1930's semi and it recently occurred to me that it might be a bit of a problem because of our airbricks and suspended floors.

Currently the whole side-wall (ie. not front/back wall) cavity is ventilated with grilles at each end of the top of the main side wall and is open into the loft (at least, the shower cable from the CU runs up the cavity and into the loft so I assume it's open). This wall is cold to the touch on the inside normally. Maybe its down to draughts rather than just conduction etc.

Filling up the cavity with fluff stuff would stop this ventilation (though I guess the ventilation is also causing a lot of heat loss). If this is the case, should I be able to remove/block up these grilles and top of cavity in loft and see less heat loss from these walls. Currently the shower extractor fan vents out one of these grilles anyway. Are there any implications with doing this?

I'm aware that I need to make sure that the floor space is adequately ventilated - I know can't block these ones up. So how can cavity insulation be added without blocking these vents?

Thanks

David

[Alex]

Cavitys are not designed to need ventilation,I would have thought that the vents were put in to vent a room and have been covered up on the inside,vents below dpc are to vent underfloor

[Martin Angove]

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Forgetting ventillation and insulation, about which I know little, you may need to check the rating of your shower power cable if you are about to surround it with insulation.

I have just done some work in a house with a similar situation. The

8.5kW shower is currently wired in 6mm2 cable which runs up an empty cavity, across the tops of joists in the attic and down into the (switch and) shower.

8.5kW at 240V is about 35.5A and given that the cable is well-ventilated, the regulations say that it will carry 47A. This is fine, but if the wall were insulated or the cable was enclosed in insulation in the loft it would have to be derated to 35A which is one of those situations where you say "it'll *probably* be ok, but..."

If you happen to have a 9.5kW shower (39.5A) then this derating should prompt you to uprate the cable. The next size up is 10mm2 which is a

*pig* to work with.

Just a thought.

Hwyl!

M.

[Marc Lee]

When we had our walls done last year, they put little plastic things in the air brick vents to keep them clear of the insulation material.

Why not check with your installer?

Marc