Quizzes & Puzzles1 min ago
Cavity wall Insulation
6 Answers
To a point I am well up on DIY, one question regards the above, does this work? I was always under the impression that the cavity circulates the air within the walls to reduce damp, am I right? we have had a damp course quote & they stated that the insertion of the Insulation starts 3 bricks down from the eves!! I have never heard of this before! is this right? If give the opportunity would you go for it? also I would think that this would also block the air bricks within the walls of the base of the house if the air bricks did not go to the inner wall all in one. a bit of advise would be welcomed.
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I've heard conflicting reports about cavity wall insulation. Some say it works; others say it causes problems by not letting the cavity do what it it was originally intended for.
However, we had ours done about 2 years ago and one thing I can say, is that the firm that did ours, replaced all of the air bricks and placed something in the cavity above each air brick to make sure that they didn't get clogged up with the insulation falling down, so if you do go ahead with it - make sure that the firm that you get does likewise.
However, we had ours done about 2 years ago and one thing I can say, is that the firm that did ours, replaced all of the air bricks and placed something in the cavity above each air brick to make sure that they didn't get clogged up with the insulation falling down, so if you do go ahead with it - make sure that the firm that you get does likewise.
Your assertion about air circulation is not my understanding and Wikipedia seems to agree.
http://en.wikipedia.org/wiki/Cavity_wall
The cavity is there as an air gap to prevent water-laden outer skin transferring some of its moisture across to the inner skin. OK, so if there is no insulation filling it, the passage of water down to ground in the outer skin is assisted because it can run down the inside of the outer skin. But with a filled cavity it will still reach the ground because of the porous nature of brick plus gravity.
The original concern about cavity insulation was the integrity of the cellular structure of the foam and being sure it wouldn't act as a sponge. After over 30 years of successful use and the support of the Buildings Research Establishment, I think most of us can be pretty certain that it works fine.
The reason of having damp courses is to prevent GROUNDWATER being sucked up from below. I don't understand your comment about quotes for damp courses involving the insertion of insulation. Damp courses involve the insertion of a chemical into the bricks low down to mimic the effect of having an impervious layer of plastic (which is what modern construction uses). This does nothing to insulate anything.
The business about air bricks; they are there for one or two reasons: -
1) To provide an airflow INTO THE HOUSE (not into the cavity), much the same opening the window in rooms that had an open fire, before the days of window vents.
2) To provide airflow under the floor level for those houses with wooden floor joists, not concrete slab. Wood needs ventilation or the floor joists will rot.
In both of these situations, an linking pipe is inserted to avoid the insulation blocking the airflow, which occurs right through the 2 skins, not just through the 1st outer skin.
http://en.wikipedia.org/wiki/Cavity_wall
The cavity is there as an air gap to prevent water-laden outer skin transferring some of its moisture across to the inner skin. OK, so if there is no insulation filling it, the passage of water down to ground in the outer skin is assisted because it can run down the inside of the outer skin. But with a filled cavity it will still reach the ground because of the porous nature of brick plus gravity.
The original concern about cavity insulation was the integrity of the cellular structure of the foam and being sure it wouldn't act as a sponge. After over 30 years of successful use and the support of the Buildings Research Establishment, I think most of us can be pretty certain that it works fine.
The reason of having damp courses is to prevent GROUNDWATER being sucked up from below. I don't understand your comment about quotes for damp courses involving the insertion of insulation. Damp courses involve the insertion of a chemical into the bricks low down to mimic the effect of having an impervious layer of plastic (which is what modern construction uses). This does nothing to insulate anything.
The business about air bricks; they are there for one or two reasons: -
1) To provide an airflow INTO THE HOUSE (not into the cavity), much the same opening the window in rooms that had an open fire, before the days of window vents.
2) To provide airflow under the floor level for those houses with wooden floor joists, not concrete slab. Wood needs ventilation or the floor joists will rot.
In both of these situations, an linking pipe is inserted to avoid the insulation blocking the airflow, which occurs right through the 2 skins, not just through the 1st outer skin.
The purpose of the cavity is, as has been mentioned, to prevent water getting throught the wall to the interior of the house. In the early days I think they were actually built to allow a slight airflow within the cavity but for many, many decades now they have been "sealed," initially completely by bricks but now by cavity closers.
Any moisture which soaks through to the inside of the cavity wall should run down the inner surface of the outer wall, and, at ground level (which is usually about two courses below DPC) should leave the wall due to a combination of preformed weepholes and a slope on the concrete cavity filling below ground level.
TWR, do you mean you have had a quote for CAVITY INSULATION (not a damp course) and that the insertion of the insulation starts three courses below the eaves, because as Buildersmate says, your question doesn't make sense as it is written.
Any moisture which soaks through to the inside of the cavity wall should run down the inner surface of the outer wall, and, at ground level (which is usually about two courses below DPC) should leave the wall due to a combination of preformed weepholes and a slope on the concrete cavity filling below ground level.
TWR, do you mean you have had a quote for CAVITY INSULATION (not a damp course) and that the insertion of the insulation starts three courses below the eaves, because as Buildersmate says, your question doesn't make sense as it is written.
Thanks for your replies, the Quote was for cavity wall insulation not damp proof, I am aware of the difference, the part I cannot suss is why do the state that the C.W.I starts 3courses down from the eaves, and yes I am aware of the air bricks & there purpose but I have heard that many conflicting stories regards the insulation that this has given me doubts, buildersmate thanks for your reply but the way I see this if the cavity is damp this in turn will be drawn into the insulation depending what type they use, this is the part I am not to sure about & is giving me 2ND thoughts. I shall have to wait & study the advise given then make my decision, again thanks all for your help.
Hello TWR, the reason they are saying three courses down is probably because due to overhanging rafters, fascias etc they use three courses as their standard practice.
Keeping three courses down will also help to prevent unsettling bricks at the top of the wall when drilling, in other words, they are making sure that when they drill they don't lift any bricks which could actually happen if they drill say, one course below the eaves, the extra weight keeping everything solid. Of course this may give you some concerns as to whether the material injected will fill to the top of the cavity. In your case I would be seeking assurances from the installers that work would be carried out to ensure this.
Keeping three courses down will also help to prevent unsettling bricks at the top of the wall when drilling, in other words, they are making sure that when they drill they don't lift any bricks which could actually happen if they drill say, one course below the eaves, the extra weight keeping everything solid. Of course this may give you some concerns as to whether the material injected will fill to the top of the cavity. In your case I would be seeking assurances from the installers that work would be carried out to ensure this.
Hi gazzawazza, thanks to you & all that have responded, believe it or not my Niece's husband is a builder & I should have asked him first but there we go, the advice from here + what he has confirmed has put my mind at rest & ill be getting it done within a couple of months, again , thanks to all that give out their advise.
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