Cavity Wall Insul;ation - does it work ?

[Stephen]

Winter's here so I'm thinking about cavity wall insulation. My house was built in 1989 of block and external brick construction but I can't tell whether there is any insulation already there (I don't remember seeing any when I made a hole for the cooker hood vent and there are no obvious drill holes in the exterior to tell of an after-build installation).

Is it worth it - does it make a difference ? I can get my small 4 bed detached done for £200 so realise it will take a few years to recoup costs. But if it makes for a warmer house right away . . .

What do you think? Thanks

[Malcolm Stewart]

I had my 1980s house done years ago - in November, from memory. Before and after the big day I recorded the temperature in a bedroom where the radiators were turned off. I had the bedroom door closed, so it's heating was by leakage from the rest of the house which was thermostatically controlled. The bedroom goes from front to rear of the house, and has external walls on 3 sides with single glazed windows back and front. The weather before and after installation was broadly similar, and I recall that my unheated bedroom was noticeably warmer after insulation was installed. Can't remember how many degrees, as it's >22 years ago! (Some years later, strict implementation of gas boiler ventilation requirements have noticeably reduced my comfort level. My boiler room was independently ventilated, but not strictly in accordance with the BS, so extra ventilation is now in place. You win some...)

[Christian McArdle]

No brainer. Do it. Make sure they're competent, so that they block holes, use full fill insulation and sleeve any airbricks.

Christian.

[Uno Hoo!]

I had my detached home cavity wall insulated some years ago - and it was well worth it. The thing to remember is that it does not necessarily make your house 'warmer' - it just reduces the amount of energy required to

*keep* it warm! What I find is that during the winter months, once the house is warmed up, the central heating switches off - and stays off - for much longer periods than it used to prior to the insulation being installed. The radiators can become cold and yet the house remains warm because the heat is retained for much longer. Don't hestitate - just go and order it!

Kev

[chris French]

In message , Malcolm Stewart writes

It'll only make it warmer if the heating system can't keep up with the heating requirements, but it will reduce the energy required to keep it warem

[sPoNiX]

Be aware that some people experience problems with damp after having cavity wall insulation installed. Cavity insulation the dew point to move..ideally this is within the cavity..when the cavity is insulated it sometimes moves into the actual building giving damp/condensation problems.

Make sure the company do a dew point calculation before starting work.

Also, a few people are affected by fumes from the foam that is used. This is rare but needs to be taken into account, especially if anyone in the household has a pre-existing breathing problem.

sponix

[airsmoothed]

We had our 1980 built detached insulated 2 years ago and the house certainly feels warmer, even with the thermostat turned down a couple of degrees. Hardly a scientific report mind you.... Plus there was some government subsidy or other on getting the work done, and the remaining cost was spread over 2 years interest free. Well worth it. All organised via the gas board IIRC.

[PeTe33]

Just had a man around this morning to quote, as our UFH does struggle more on the really windy/wet 10 degree nights than the dry & not windy 5 degree ones. Not having _any_ loft insulation doesn't help mind, but there is still a bit more electrical work to do up there before bedding it down.

Re: Grants, he told us to hold off on the Loft insulation as there doesn't seem to be any grant money available (with them at least) until about January; after which he believed grants would only be available on properties with zero insulation rather than those that needed a "top-up".

Same thing would prolly apply with cavity grants, but I'm certainly not going to wait until the depths of winter to get the walls done.

[Andy]

They use blown cavity-grade rockwool too.

Andy.

[Dave Fawthrop]

| Also, a few people are affected by fumes from the foam that is used. | This is rare but needs to be taken into account, especially if anyone | in the household has a pre-existing breathing problem.

My house was done with foam, and we did not even smell these hypothetical fumes. We had no problems except that I had to cut away lumps of overspill foam in the underdrawing which are still there.

[dg]

The installation of cavity insulation will make the internal wall surface warmer, and is unlikely to cause any internal or intersitual condensation issues. In addition the increase in average internal room temperatiures will hold more moisture in the air

A calculation of relative humidity before starting work is pointless

Some older pumped foam installations would cause bridging of the DPC inside the cavity, and effloresence to external brickwork at DPC level

I did not think that foam was used now, it seems to be either dry fibre or to a lesser degree polystyrene beads.

dg

[Nick H]

Are you sure you haven't already got cavity fill ?

I know that houses I was building at that time were all cavity filled the regs on insulation values were getting quite strict and most house were cavity filled with "thermalite" type blocks. I remember that yo could get around the cavity fill by using a thicker block. I woul double check that you haven't already got insulation.

If you haven't I would say definately get it done. I had my house wall done with rockwool and increased the loft insulation to 8" and th difference is amazing. We need very little heating to keep the hous cosy now

-- Nick H

[Michael Chare]

The cost is subsidised which helps.

If your house is at all prone to attracting green mold, then you may get more of this.

[sPoNiX]

Yes, there are alternatives, problems are rare and it is generally worth having done.. However, make sure that the company does all the correct calculations before starting work.

sponix

[The Natural Philosopher]

Not quite. Experiences with solid brick, cavity and cavity imnsualted houses suggest that (assuming other things like draughtproofing and roof insulation are done first) the cavity wall insulation improves the interior wall temperature: In short the cold spots go...and so the overall room temperature can be reduced without compromising the colder areas.

That's has always been my experience of well insulated houses. More EVEN temperature, and more confort, at a lower temperature.

[Christian McArdle]

Yes. It is due to relative levels of radiant heat from the walls. If the walls are warmer, it feels warmer, even for the same air temperature. So insulation has TWO beneficial effects for comfort/efficiency.

The energy used is proportional to the product of u-Value and air temp.

Insulation not only reduces the u-Value, but because of the greater comfort provided for the same air temperature, allows a lower air temperature to be used, reducing energy usage further.

Christian.

[Doctor Drivel]

thermostatically

Cavity wall insulation reduces/eliminates cold spots, making the house much warmer and more comfortable.

[Christian McArdle]

I should have said air temperature difference...

Christian.