part L1b - insulation solid walls

Postby myHouse » Sat Sep 19, 2009 12:46 pm

Hello everyone

I have just stripped my 105sqm 1900s 3 storey house back to bare brick as it had damp problems. I was planning to replaster throughout (using sand and cement render for lower ground floor) A builder would be doing the work. I have since learned that i will have to insulate the whole house to ensure u values are 0.35 or less if this is to comply with building regs. I am on a very tight budget - does anyone have any idea how i could achieve compliance (eg exact materials) and idea of cost. Also on such an old building would not the insulation encourage more damp? I have trawled the internet for 3 days now trying to find a simple solution but am confused with everything.

Any ideas on a budget product that would do the job simply

Thank you for your help
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Joined: Sat Sep 19, 2009 12:37 pm


Simply Build It

Postby Perry525 » Wed Sep 23, 2009 7:22 pm

You have read L1b and know what is required.
Basically you have a choice between insulating inside or out.
If you go to work and are out all day and you turn the heating off then insulating on the inside will work for you. It warms up quicker.
If you are there all the time and the heating is on all the time then having the insulation on the outside is good as the walls will act as a heat store and this will be more economic.
As far as damp is concerned, if there is not a problem with the roof, pipes or damp proof course, either will do.
But, you mention using sand and cement render on the ground floor. Why are you doing this?
Walls built in 1900 would not include cement.
Cement render will be too hard and will crack.
Only use lime based render.
Better still use Browning and Thistle.
Probably the best solution is buy polystyrene or Jablite and glue it to the walls on the inside and plaster over.
More expensive is Celotex with plasterboard already attached, merely glue it in place and skim coat.
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Postby myHouse » Thu Sep 24, 2009 7:43 pm

Thanks Perry525 for answering my post - very grateful for your input.

A builder told me that to keep the damp and hygroscopic salts from coming through once decoration is done i should use a sand and cement render. The house was previously flooded and there is lots of salt in the wall apparently and this is attracting or holding moisture in the wall.

I dont think i could render externally as it is in a row of terraces and the layer of insulation and render would stick out from the houses either side.

Lime based render, browning and thistle? would not these cost much much more to apply (by special craftsmen) as compared to normal stuff?
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Joined: Sat Sep 19, 2009 12:37 pm

Postby Perry525 » Fri Sep 25, 2009 5:32 pm

Unfortunately bricks and mortar soak up an enormous amount of water, that can take as long as three years to completely dry.
I can understand that you do not want to wait that long before decorating.
Never the less, when your home was built, they would have used a lime based mortar, lime based mortar is a wonderful product, in as much as, it allows the home to move, as the year rolls round the home expands and contracts with the heat of the sun and the cold of winter.
A cement based render, will not move the same way and will create friction and will crack.
Lime based render and a browning are the traditional bases used as they have a degree of flexibility.
The interesting thing about damp is that it always moves towards cold, keeping the rooms warm will ensure that the damp moves outwards and blows away in the wind.
If you turn the heating off and allow the rooms to become cold then the damp will come in.
Whichever way it goes, the water vapour/damp will have to go somewhere and will probably end up staining the walls.
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Joined: Fri Jul 06, 2007 7:35 pm

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