Airtightness & Ventilation
Ventilation is vital - without it we would all suffocate, however a huge amount of heat is lost from our homes through ventilation.
Ventilation takes two forms:-
Obviously you want more of the first than the second!
There is a phrase in the eco building industry -
"Build tight and ventilate right"
Whilst in reality it is almost impossible to make a house so airtight that you would die, as you make efforts to reduce unintentional ventilation it becomes vital to ensure that the intentional ventilation is provided correctly. Without this all sorts of problems start to occur such as stuffiness, condensation and mould which are all harmful to health and well being. Below are the steps we have taken to improve the ventilation of our home.
Ventilation takes two forms:-
- Intentional e.g. extractor fans and window trickle vents
- Unintentional e.g. drafts
Obviously you want more of the first than the second!
There is a phrase in the eco building industry -
"Build tight and ventilate right"
Whilst in reality it is almost impossible to make a house so airtight that you would die, as you make efforts to reduce unintentional ventilation it becomes vital to ensure that the intentional ventilation is provided correctly. Without this all sorts of problems start to occur such as stuffiness, condensation and mould which are all harmful to health and well being. Below are the steps we have taken to improve the ventilation of our home.
Increasing Airtightness
Windows
Window frame showing aluminium tape for airtightness
The original sash windows had been replaced with uPVC double glazing when the house was refurbished in 2000. The units themselves were reasonable quality however they had been badly fitted. All the developer had done was take out the sash panels and replace them with the plastic units. All of the rest of the sash window such as the wooden frames and the pockets containing the counterweights had been left and clad in plastic both inside and out.
In the six years between the refurbishment and us buying the house, a lot of water had worked it's way under the plastic cladding and some of the frames had severe rot. The frames were also clearly not airtight as the wind could be heard whistling around the windows at night
We would have dearly loved to have restored the original windows, but we could neither afford it or warrant throwing away perfectly servicable double glazed windows. Even though we didn't particularly like the look of uPVC, we could not justify sending them to landfill, so I set about trying to repair the damage caused by the cladding and try and make them airtight.
The exterior of the frames was fairly easy - just a combination of wet rot hardener, wood filler, frame sealant and paint, however the interior was more difficult.
Removing the plastic cladding inside revealed that there was a 5-10mm gap between the uPVC units and the old frames. This was causing both drafts and a lot of noise through the windows. Filling this gap with expanding foam stopped the drafts and reduced the noise significantly - it also has an insulating effect. If you are using foam to fill gaps around windows and doors then please use it sparingly as it expands to many times it's original size. Put to much in and it'll expand too much and you stand a real chance of buckling your frames if the foam can't escape quickly enough. In order to avoid this I used low expansion foam specially designed for windows which I bought from Screwfix. It is also delivered using a sealant gun rather than an aerosol can so it is much more controllable.
Once the foam had cured and been cut back using a stanley knife, it was time to tidy up the internal frames. The foam should have been sufficient to stop any drafts however I decided to make sure by using tape to make an airtight seal between the wooden frames and the PVC units. You can by specialist air-thightness tapes for this, but they are expensive, so I used Class O aluminium tape tape instead. This is designed for sealing ventilation ducts and units, so is airtight and can be bought from Screwfix and other building merchants at around £10 for 100 meters (compared to £1 a meter for most specialist air-tightness tapes). I also tried this tape from Wickes which is used to seal joints between insulation, it's only £5 a role but it seemed much less robust.
In the six years between the refurbishment and us buying the house, a lot of water had worked it's way under the plastic cladding and some of the frames had severe rot. The frames were also clearly not airtight as the wind could be heard whistling around the windows at night
We would have dearly loved to have restored the original windows, but we could neither afford it or warrant throwing away perfectly servicable double glazed windows. Even though we didn't particularly like the look of uPVC, we could not justify sending them to landfill, so I set about trying to repair the damage caused by the cladding and try and make them airtight.
The exterior of the frames was fairly easy - just a combination of wet rot hardener, wood filler, frame sealant and paint, however the interior was more difficult.
Removing the plastic cladding inside revealed that there was a 5-10mm gap between the uPVC units and the old frames. This was causing both drafts and a lot of noise through the windows. Filling this gap with expanding foam stopped the drafts and reduced the noise significantly - it also has an insulating effect. If you are using foam to fill gaps around windows and doors then please use it sparingly as it expands to many times it's original size. Put to much in and it'll expand too much and you stand a real chance of buckling your frames if the foam can't escape quickly enough. In order to avoid this I used low expansion foam specially designed for windows which I bought from Screwfix. It is also delivered using a sealant gun rather than an aerosol can so it is much more controllable.
Once the foam had cured and been cut back using a stanley knife, it was time to tidy up the internal frames. The foam should have been sufficient to stop any drafts however I decided to make sure by using tape to make an airtight seal between the wooden frames and the PVC units. You can by specialist air-thightness tapes for this, but they are expensive, so I used Class O aluminium tape tape instead. This is designed for sealing ventilation ducts and units, so is airtight and can be bought from Screwfix and other building merchants at around £10 for 100 meters (compared to £1 a meter for most specialist air-tightness tapes). I also tried this tape from Wickes which is used to seal joints between insulation, it's only £5 a role but it seemed much less robust.
MDF clading showing expansion gap which will be filled
I quite like the space age look of the metal tape, but I'm told it doesn't really go with the period vibe of the house, so once the frames were completely airtight, the tape was covered with 3mm MDF sheeting. I left a small 2mm gap between the PVC unit and the new MDF cladding which was filled with flexible caulk. This is because PVC expands a lot more than wood in hot weather and I wanted to ensure that the airtight seal was maintained
Costs (for airtightness measures only)
Expanding foam £40 for 4 cans - one can does two windows
3mm MDF £21 for 3 1200 x 600mm sheets
Class O Tape £10 for one 100m roll
Total £71 for 8 windows
Impact
There are noticeably less drafts from the windows and noise levels from outside have been massively reduced
Was it worth it?
This was quite a big job and I haven't finished all of the windows yet, but I believe it was worth it. Not only have we improved the thermal comfort, but as a light sleeper I have found the noise improvement a godsend.
Costs (for airtightness measures only)
Expanding foam £40 for 4 cans - one can does two windows
3mm MDF £21 for 3 1200 x 600mm sheets
Class O Tape £10 for one 100m roll
Total £71 for 8 windows
Impact
There are noticeably less drafts from the windows and noise levels from outside have been massively reduced
Was it worth it?
This was quite a big job and I haven't finished all of the windows yet, but I believe it was worth it. Not only have we improved the thermal comfort, but as a light sleeper I have found the noise improvement a godsend.
Doors
Before - big hole
Just like the windows, the original external doors had been replaced with uPVC. The back door had been placed into a new opening so was a snug fit, but the front door was surrounded by more plastic cladding which I had now learned was generally used in the double glazing trade to hide all sorts of horrors.
It was therefore with some trepidation that I removed the exterior cladding. Upon doing so I found a 60mm wide gap between the door frame and the wall filled with...... nothing. You could fit your hand in it - no wonder there was such a draft coming through by the door!
Out came the squirty foam again, although this time I used the normal high expansion variety as the gap was so big I had no fear of it not having room to expand!
Whilst I was examining the door in detail I spotted that the draught seals in a few areas were not fully sealing so I added some additional foam strips to the door.
The difference in drafts and noise was immediately apparent. It was also noticeably warmer by the door - presumably due to the increased air tightness and the added insulation due to the foam.
It was therefore with some trepidation that I removed the exterior cladding. Upon doing so I found a 60mm wide gap between the door frame and the wall filled with...... nothing. You could fit your hand in it - no wonder there was such a draft coming through by the door!
Out came the squirty foam again, although this time I used the normal high expansion variety as the gap was so big I had no fear of it not having room to expand!
Whilst I was examining the door in detail I spotted that the draught seals in a few areas were not fully sealing so I added some additional foam strips to the door.
The difference in drafts and noise was immediately apparent. It was also noticeably warmer by the door - presumably due to the increased air tightness and the added insulation due to the foam.
After - The broken bit at the top was intentional (honest!)
The cladding was then re-attached using frame sealant - hiding the horror that now was a foam filled, but airtight gap!
The letter box also had some foam draft strip added to its flap to ensure that it made a better seal.
Costs (for airtightness measures only)
Expanding foam £5 for 1 can
Frame sealant £4 for 1 tube
Draft strip foam £5 for 15m
Total £14
Impact
As with the windows there are noticeably less drafts and noise levels from outside have been massively reduced.
Was it worth it?
For such a quick job which took less than an hour I am amazed with the results.
The letter box also had some foam draft strip added to its flap to ensure that it made a better seal.
Costs (for airtightness measures only)
Expanding foam £5 for 1 can
Frame sealant £4 for 1 tube
Draft strip foam £5 for 15m
Total £14
Impact
As with the windows there are noticeably less drafts and noise levels from outside have been massively reduced.
Was it worth it?
For such a quick job which took less than an hour I am amazed with the results.
Improving Controlled Ventilation
Heat Recovery
"How the hell is this going to fit in the loft....."
We are currently in the final stages of installing a Mechanical Heat Recovery Ventilation system in the house. Update coming soon!
