filling a cavity wall which has already got cavity bats?

[mpooley]

I am trying to get as much insulation into my house as possible.
sooo]

what do people think about filling a cavity wall which has already got cavity bats?
my cavity is about 70mm and I think the bats are 25mm so surely its possible?

?

mike

[pb]

I am trying to get as much insulation into my house as possible.
sooo]

what do people think about filling a cavity wall which has already got cavity bats?
my cavity is about 70mm and I think the bats are 25mm so surely its possible?

The main purpose of the cavity is to make sure that any water which gets through the outer leaf of the wall ends up running down the inside of the cavity and can't cross over to the inner leaf (from where it might penetrate into the building).  If you fill the cavity, or reduce the gap too much, you will obviously remove this barrier which will increase the risk of dampness on the inside.  How big a deal this is in practice would depend on how watertight your outer leaf is and how much exposure it has to driving rain.

With only a 70mm cavity it might also be difficult to disperse the insulation effectively without creating voids.  If you have access from above then you could probably pour in vermiculite or similar without too much trouble.

Personally I would leave the cavity alone and put extra insulation on either the inside or outside of the walls if at all possible.

[mpooley]

Inside most of it is impossible to insulate - externally would be extremely expensive i would guess.
my house is an old renovated barn so walls vary some are brick some are stone its a nightmare 

[A.L.]

hi,

if brick/cavity/batt/brick  you have a U - value of about 0.81, filling the cavity will reduce it to about 0.43,

while this is done, either accidentally or deliberately by an installer any CIGA (www.ciga.co.uk/) guarantee issued will be invalid, although  I have not known any problems arise

[mpooley]

hi,

if brick/cavity/batt/brick  you have a U - value of about 0.81, filling the cavity will reduce it to about 0.43,

while this is done, either accidentally or deliberately by an installer any CIGA (www.ciga.co.uk/) guarantee issued will be invalid, although  I have not known any problems arise

Thanks
I am going to ask an installer to come and have a look I think.
Oh and where do you get your figures for u-values from please?

[A.L.]

Oh and where do you get your figures for u-values from please?

- I have some energy audit software 

[wookey]

It's very easy to work out your U-values here: http://www.vesma.com/tutorial/uvalue01/uvalue01.htm

[mpooley]

thanks wookey thats very handy 

[Other-Power]

I have recently had bonded bead installed and speaking to the chap who surveied saud that the binded bead is ok to fill up remaining space on walls with little or no insulation.  the only limit here is making sure the house is outside of the warranty.  I would ask the energy saving trust to find a company near you that does bonded bead.

Cheers

Jon

[mpooley]

Thanks
I have had a guy look at it and he says that the cavity is full so I didn't need it after all.
 

[clivejo]

Do you mean Bats as in the flying mice?  If so they are protected by law :

http://www.bats.org.uk/pages/bats_and_the_law.html

[biff]

Cavity bats are normally a brown fibre matt 18" x 4ft x 2", these are built in by the brickies during construction.We always considered them cheap and nasty and would always recommend kingspan insulation which can interlock properly.The cavity batts have a habit of sagging and sliding out of place unless well clipped into position.
                                       Biff