Blow in insulation is a fairly self-explanatory term. It basically involves a specialist firm drilling holes in the outer leaf of your cavity wall in order to pump in insulation.
This insulation then fills the cavities making your house easier to heat by retaining the heat for longer.
Blow in insulation can only be retro-fitted to traditional cavity walls (where you have a masonry inner leaf and a masonry outer leaf).
If you add it to a timber frame house (in the UK), when you sell it the mortgage surveyor will likely say it’s not suitable for mortgage purposes (as they are directed to do so by the lending institutions).
So, why can’t it be installed in a timber frame house in the UK but it's ok in timber frame houses in the USA?
To be honest I’m not completely sure!
There was a report in the 1980’s where some timber frame houses in Scotland were filled with blow in insulation and the report focused on the potential damage that could be caused by the blow in insulation allowing moisture to penetrate and/or condensation to form against the frame and ultimately causing rot to the timber frame.
There have been many articles written over the years questioning the validity of this report and whether modern blow in EPS (expanded polystyrene) bead insulation would cause the same issue.
Personally I suspect the confusion has occurred from the different types of blow in insulation available. In the eighties it was more common to use mineral fibre wool as a blow in insulation rather than EPS beads (although these were used as well).
Either way, the lending institutions in the UK have instructed their valuers that the addition of cavity insulation to a timber frame property should be notified to them in the mortgage report. If it is detailed on the mortgage report, none of them (as far as I'm aware) will lend on these properties.
In my opinion the use of fibre insulation (Fibreglass wool or Mineral Fibre wool) and Cellulose as a blown in insulation is a bad idea for several reasons:
Today the use of fibre and Cellulose is thankfully less common as a blow in insulation (although it is still used). Instead the most common form is expanded polystyrene (EPS) beads. In the past they were typically white but now they're normally grey. The main difference with the grey beads, apart from the colour, is they have a slightly lower u-value (lower is better).
As I see it, there are many advantages to upgrading your existing home by installing blown in insulation (but not with fibre, cellulose or spray foam):
For more information not he advantages and disadvantages of cavity fill insulation see my article on the issues here.
When installing blown in insulation, your chosen company should carry out an initial survey to confirm that your home is suitable and provide you with a cost of installation.
Then on the day of installation they'll drill holes in the outer leaf of your external walls. These will mainly be at the top of the walls so that the beads will fall to the bottom and fill the cavity. They will however drill holes beneath all the window sills to ensure these areas also get filled properly.
Once they have the cavities filled they’ll fill the holes and match the finish to the surrounding finish as best they can.
As with anything there are some precautions that should be noted before going down this route. But thankfully there aren’t that many.
I suspect the initial concerns from the 1980’s report mentioned above, may have been worried about mineral fibre wool as a blow in insulant for timber framed building. If that’s the case I would have the same concerns, however I can’t see how EPS beads would create the same level of concern.
Unfortunately I can’t imagine the lending institutions will take any notice of my opinion and with the entire industry against the use of blow in insulation on existing timber frame properties I suspect nothing will change.
However if you have a traditional cavity house with part or no insulation then blow in insulation is a cheap and effective way of increasing the thermal efficiency of your home significantly.
If you're still not convinced have a look at my article on the best types of insulation for homes for more ideas including loft insulation and rigid foam insulation etc.
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