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

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

In message ,
(Swampie) wrote:

I've been thinking about cavity wall insulation

[...]


Currently the whole side-wall [...] cavity 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).

[...]

Are there any implications with doing this?


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.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... If flies couldn't fly, would they be called walks?

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

(Swampie) wrote in message om...
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