We're renovating our living-room and have stripped the walls down to the brick.
Before re-plastering I'd like to insulate the external walls (solid brick walls). I have spent the day trying to determine what is the best material to use and am none the wiser!
Ideally I'd like to know which material gives the best insulation, comparing like-for-like thickness.
I don't want to add too much thickness to the walls - perhaps 25mm max?
I rang the energy saving trust and they told me the best thing would be Sempatap thermal lining, but I'm not so sure. I don't have a way of comparing it with other materials. They told me the U value of it is 1.58 W/m2K.
The thermal conductivity (I don't know if that is the same thing as U value) of acoustic plasterboard is 0.24W/mK.
Celotex Celotex PIR Insulation Board (25mm) as sold at Wickes apparently has the same level of thermal insulation as almost twice as much glasswool insulation.
I saw that glasswool insulation has a thermal conductivity of 0.04 W/mK, so I'm guessing the Celotex has 0.02 W/mK? Which sounds much better than the Sempatap, assuming that U-value and thermal conductivity are the same thing.
I saw expanded polystyrene thermal board has thermal conductivity of 0.038 W/mK.
I saw somewhere that the thermal conductivity of ordinary plasterboard is 0.16 W/mK.
Now I'm writing this out it looks to me like the Celotex is the best option, assuming thermal conductivity and U-values are the same.
So here are my questions:
Are thermal conductivity and U-value the same thing?
If not, how do I convert from one to the other?
Does anyone have any tips for comparing different materials?
To get to U value from thermal conductivity you need to divide by the thickness of the material.
TC of glass wool is 0.04 so 100 mm would give a U value of 0.04/0.1=0.4W/m2K. 250 mm would give 0.04/0.25=0.16.
I would not recommend you put anything other than a masonry type of coating with a breathable paint on an external solid brick wall. If you put any covering on the wall which traps moisture condensation this will form on the relatively cold wall. With a porous wall in cold conditions water will appear at the bottom edge of the wall, soaking carpets, rotting skirtings, wetting structural timbers fitted into the wall and associated problems.
“To get to U value from thermal conductivity you need to divide by the thickness of the material. “
Thanks, Stoneyboy, I'm very grateful for your explanation because now it's all fallen into place and makes perfect sense! It also explains why thermal conductivity is in W/mK and U value is in W/m²K. **
For my purposes, then, I should look at the thermal conductivity because I want to see which material is best for the same thickness.
So Sempatap (10mm thick) would have thermal conductivity of 1.58 * 0.01 = 0.0158 W/mK which makes it the best insulator out of all of them, with Celotex not far behind at 0.02 W/mK if my calcs are correct.
“I would not recommend you put anything other than a masonry type of coating with a breathable paint on an external solid brick wall. If you put any covering on the wall which traps moisture condensation this will form on the relatively cold wall. With a porous wall in cold conditions water will appear at the bottom edge of the wall, soaking carpets, rotting skirtings, wetting structural timbers fitted into the wall and associated problems. “
Yes, I saw you'd written that in another post and I feel a bit anxious as I certainly don't want to have problems in the future.
Are you saying that you don't recommend putting insulation on a solid brick wall?
But how will the insulation trap moisture?
The person at the company which sells Sempatap told me the wall should be skimmed first, so if there are no gaps between the wall and the insulation shouldn't that be OK? Similarly for thermal board?
Many TIA for answering my questions.
** For others reading this, m2 should be meters squared, but I don't know how to format the 2 to look like a square as HTML doesn't seem to work here.
Ah, wait, Alt+0178 may do the trick!
Are you saying that you don't recommend putting insulation on a solid brick wall? Yes, probably not what you wanted to hear.
You can skim and seal a solid wall which will stop moisture reaching the inner surface of the wall but only in the areas treated. Walls which join the outer wall and areas between floors will become wetter.
The main problem will be condensation, once a solid wall is covered with insulation it becomes colder and attracts more moisture. Even if a DPM is incorporated in the covering (eg plasterboard with integral foil dpm) damp in the vapour phase will still get to the cold wall through joins in the boards or around the edges of the boards. If the insulated outer wall abuts a carpeted concrete floor the condensation will show as a damp edge along the carpet.
Unfortunately there are many energy-saving measures being promoted without the long term consequences being considered.
Yes, you could insulated your solid wall and short term the wall and house will be warmer. I cannot say for definite that a damp problem will arise, there are too many variables eg water penetration of the external wall; temperature and humidity in your house; exposure and orientation of the external wall; outside temperature etc. In my experience insulating a solid exterior outside wall without measures to remove water/condensation can lead to serious damp problems.
Supposing you did carry out insulation and 5 years later you have serious rot problems with structural timber adjacent to the wall. Do you think either of the official bodies you have mentioned will put things right?
Another example of potential long term problems is the addition of extra insulation in a loft. If this done and cables are encased in the insulation this contravenes regulations and can be a safety issue.
The same issues can be applied to cavity wall insulation if this encases cables.
You're absolutely right about it being important to consider long-term consequences, and that's why I've written to the bodies concerned, because I think it's important that they are aware of the isssues you have mentioned before they make recommendations.
In my case I live in a terraced flat and the external wall in question isn't very big (and half of it is window anyway) so in the end it's not a big deal if I don't insulate it - I just thought it would be a good idea to save on heating bills. In light of your advice, I've reconsidered!
If you decide to use a laminate the most thermally efficient product is phenolic foam. I know as I used to sell then several years ago.
I would recommend you speak to Encon Insulation. Ian (of Encon) is the most knowledgeable guy I know in the industry and he can do free calculations to determine if you have a potential condensation problem.
Two things I will say is phenolic is a great product and has great fire resistance properties however if you screw fix you will need stainless steel fixings as carbon steel will react to the phenolic or alternatively it would be cheaper to dot and dab it to the walls.
However please note phenolic may be the thinnest insulator but it is also one of the most expensive so you may wish to consider trading product thickness against cost, in which case Ian should be able to give you a few alternatives such as extruded polystyrene or polyurethane.
There are many energy-saving measures being promoted while planning for any type of construction inside or outside.
I also agreed with stone boy the main problem will be condensation while construction. :P
Water vapour that is created by you, in your home by washing, cooking, breathing..........must be dealt with.
If you have an extractor fans in your kitchen and bathroom and if you use them, when and after cooking and washing than most of the water vapour will move outside, however a basic extractor fan is not recommended as they work by pushing the warm air from the home and by pulling cold possibly wet air from the outside through holes and cracks in the homes fabric.
Extractor fans with heat exchangers and built in humidistats are best as they swap equal amounts of wet inside air for outside air (but see below) with out dragging cold air into the home through the various gaps and cracks and causing drafts.
If you open the windows for ten minutes in the morning, then a lot of the water vapour will move outside and be replaced by colder drier air. This does not always happen as sometimes the air outside and the air inside are at, or are close to the same temperature and or humidity.
You can of course buy and use a large dehumidifier, this is guaranteed to work as it merely rotate the same air that is indoors removing the water vapour, keeping the same air moving but, does not provide fresh air or remove smells.
The final point is that water vapour like heat, always moves from hot to cold.
This means, that if you insulate your outside walls by sticking 25mm polystyrene to them, making sure that you cover the entire wall side of the polystyrene with plasterboard adhesive, taking care to leave no gaps, then you will improve your heat loss through the walls by about 90% and you will leave no gaps for water vapour to move through or condense in.
One of the two large manufacturers of insulation makes a proprietary insulation product that has plasterboard stuck to their version of polystyrene, if you use this it will then only require a skim coat of plaster to finish.
Water vapour is a very fine gas, that can move through most of the things that houses are made of.
But, because it mainly moves from hot to cold if it does enter a solid wall it will merely make its way through to the cold outside.
I don't claim to be any sort of expert, I just found the suggestion that insulation leads to condensation interesting. Condensation forms on a colder surface as the moisture holding capacity of a cold surface (or cold air) is lower than a warm one, thus you get less condensation on the inside of a double glazed unit than a single glazed window. The problem is if the double glazing unit seal is broken then condensation will form on the inside of the unit between the pains. Likewise if a wall is better insulated it's internal surface temperature will be relatively warmer than if it was more poorly insulated, so logic would follow you would get less condensation forming on the inside surface. It would seem that the problem with most peoples attempts at insulating is that they leave air gaps/pockets between the insulation and the wall where condensation forms on the cold wall in the cavity and if the space is not ventilated the condensation will rot timber studwork, and rust steel screws & nails etc.
Alternatively come up with a system as with the cavity wall with a wet outer and dry inner wall that never touch. (I appreciate they still have metal wall ties joining them, but no system is perfect)
Thus to conclude if you can insulate a solid wall without leaving air gaps and try to avoid materials are adversely affected like timber & steel then condensation should be reduced, or am I wrong?
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