How to turn a lovley old house with solid walls into a warm efficient home



Fitting the wall insulation

Internal wall insulation, aerogel, eco home, greenI had made the decision to insulate my walls, internally. I was keen to keep the insulation as thin as possible to minimise loss of room space and also to prevent the need for me to move doorframes. Following plenty of research I decided to use aerogel blanket. I had the offer of buying the blanket as a roll, fixing it to the wall and then applying a mesh and render directly to the blanket. (There are examples of this being done on the web, and I spoke with someone that had done such work and could supply me the blanket). However, this seemed fiddly, so when I came across a product called Magnaline Superslim. It is the same aerogel blanket but fixed to a 9mm magnesium silicate board. The thickness of the insulation blanket was 10mm, but several thickness could be built up. I spoke to the manufacturers and received vapour permeability details from them. I used these figures for the WUFI modelling - all was good. 

The product was the best insulating product on the market, meaning I could get maximum insulation from the thinest material. Unfortuantely, the product was also very new, so it came with a hefty price tag. On avaerage, a solid 9" brck wall has an insulation U value of around 2.0 - A new build cavity wall around 0.3. I chose to use 20mm insulation on a 9mm board. This would give me a U value of about 0.5. I considered this to be an acceptable compromise. I could have added a further 10mm of insulation, but each extra layer offers diminishing returns and going thicker would mean my doorframes would need moving. I chose that I would start by insulating the rooms downstairs - The lounge, hallway and snug. 

My insulation boards woldl be 29mm thick (20mm insulation and a 9mm board). In order to fit my insulation without taking up extra room space and also to fit around doorframes I would have to remove all the plaster and render from the walls and get back to brick. A messy, horrible job. The insulation boards would be fitted tightly to the walls so I then applied a lime mortar skim to fill in any hollows, otherwise the boards may not have sat firmly or flat against the wall.

Aerogel, lime render, ecoThe boards came in standard 8'x4' sheets. The magnesium silicate board is hard and insulation backing is like a heavy blanket and very weird to touch, as if the material is super dry. Being expensive, I wanted to ensure I was as economical as possible with my cutting. The boards are cut with a hand held circular saw. I can hardly state how horrible they were to cut. I did all my cutting outside but it was essential to wear gloves and facemask. the amount of dust created is considerable and it is a particularly horrible dust. the silicate board also splinters slightly on its edge so you also needed good protactive glasses. I did have a vacuum extraction attacged to my circular saw but the insulation, being more like a blanket, tended to rip slightly with the saw and fibres quickly clogged up the extraction. It was a thoroughly disgusting job. Unfortunately, I had a lot f board to deal with.


Slowly (it's not only a horrible job, but a slow one!) the boards were fitted. I was keen that the boards should fit tightly together - after all it is insulation and you don't want gaps. The boards, when purchased, have the insulation blanket a few milliimeters larger than the silicate baords. This means that when you butt two boards together the insulation binds quite nicely. However, when you cut the board with a saw the insulation and board are cut the same length. It meant more fiddle, but I would cut the boards to size then reset the depth of my blade on the circular saw and, using a guide, trim a few millimeters off the silicateboard only so the insulation was slightly proud. by doing this I ensured that the insulation fitted tightly - I could deal with a small gap in the actually facing boards.

Magnesium silicate board, aerogel, insulation, wall, eco, green deal

Aerogel, wall insulation, green, ecoAerogel insulation boardThe boards are held firmly to the wall using metal or plastic fixings that are hammered through the board and into the wall. The fixings come in various lengths to suit. The shaft of the fixing is split so it is hammered into a slightly undersized hole to grip. The board is held in place and then you drill right through the board, insulation and into the wall to the appropriate depth. I found that eight fixings worked well on a full board, taking care not to drill too close to the edge. As I had a good, firm and flat wall, this worked well but otherwise the board would have distorted and bowed as the fixing pull the board tight into the wall. It is important the boards are held tightly without 'bounce' as this would lead to problems when plastering the boards. I found that as I had cut the boards slightly smaller than their insulation backing the insulation butted together tightly but a small gap was left between the silicate boards. Filling these gaps with expanding PU foam tightened the board even further.

© Christopher Thompson