Hi, I have a bungalow built in the 1960s which has a suspended wood floor. I’m interested in cavity wall insulation but I don’t want the insulation to block the vent bricks for my suspended floor causing potential issues in the future. I assume in the 60s the external vent brick vented into the cavity and then another vent brick was installed opposite on the internal skin to allow airflow under the floor. Would my only option be to remove the external vent brick and fit ducts?
They are called telescopic under floor vents. You would need to cut the floor up inside to install them. I would spend a lot of time researching the addition of cavity wall insulation before you commit to it. Then hopefully you will decide against it.
Yes, you can get PVC sleeves to go behind air bricks to bridge the cavity, fit them from inside under the floor if the joists don't get in the way.
You assumption of the cavity been vented via the airbrick, is more than likely erroneous, clay liners can be found crossing the cavity in properties much older. IMHO retrofitting cavity insulation is a very bad idea
I used a bright torch to look through the air brick and my air bricks are not venting the cavity. It’s not a clay liner, it’s either brick or mortar, but I was able to see it is ducted through to my suspended floor correctly. that was my main concern for insulating my cavity.
Ask yourself why we have cavity trays, weep vents, drip points on cavity ties etc. - yes! it's because the building is designed to occasionally have water flowing down the inside of the outer brick skin - either penetration or condensation. Now ask yourself what happens when you fill the cavity.
Your main concern should be the damp and mould that will no doubt occur on your internal walls when you've had the cavity insulation installed.
I've had retrofit CVI on different houses I've lived in last two decades without any problems of damp etc at least so far. It is amazingly effective, when installed correctly.
I’ve just received a price, it’s been pretty hard to get a quote. I guess many companies have been busy with the green energy grant. the price seems excessive; 1200 for a detached bungalow. I don’t know what the average prices are?
I know your trying to be green etc but it’s going to take a long long time to recoup that £1200 in energy savings.......just saying.
We are going off track a little bit, is 1200 about the average price for a detached bungalow to have the cavity walls insulated?
Sorry, cant comment as I've never had it done. Maybe like you would with any other work get a few quotes in and then compare and make a decision based on that. Is it worth contacting your council to see if any grants are available?
I paid about that last time. I think it’s better to pay for a quality job than a crappy part fill bodge, if that’s any help. Also make sure the estimator has taken good consideration of your location in product selection. It’s also important to keep pointing in good condition so you might want to factor some work in that respect also. re comfort - it does make a big difference. The internal skin of the walls becomes part of the thermal mass of the building, since most the loss will be through the floor and windows once installed. Rooms will feel warmer because the wall surface temperature will be closer to the air temperature and obviously require less heating. This might also make the property ready for an air source heat pump due to lower radiator surface temperatures required. In my experience having an ASHP also has improved comfort because it needs to be run steadily basically all the time. So the house is always comfortable. However they will cost more to run than gas, maybe not if you are adding cavity insulation and new windows etc as part of it.
There is a good article here. https://www.ovoenergy.com/guides/energy-guides/the-ultimate-guide-to-cavity-wall-insulation.html In 2018, 70% of homes with a cavity had CWI fitted.