External Wall insulation - Be aware of the risks

Djwuk

Having seen the news this morning that more money is available from the government for external wall insulation, I thought I would share my research on the subject.

Last year I applied and got £6500 reserved towards such work. Final quotes for the work came in at £17k , so I would have to find £10,500 towards it.

Having a Victorian property with solid brick walls I started to do some research on implications of external wall insulation, there is lots of information out there , but this one PDF from English Heritage sums it up best.

(I'm not allowed to post links at the mo so Google "English heritage solid wall Insulation")

Based on this research and finding that external insulation provided under the government schemes struggles to prove its "breathability", I decided the risks of causing serious damage to the building too high. I declined the £6500 grant.

I did look at internal insulation, but this is just as complicated with vapour barriers and thermal bridging etc. The most suitable systems using breathable materials was just too expensive.

So in summary, lots of old buildings just can't cope with being insulated, without causing future problems. There are specialists who can help, but it's going to be very expensive.

In the end I installed a wood burner and have just accepted my heating bills are going to be more expensive than a modern house.

Just my humble and hopefully of use to some others

Dave

sheffield_lad

There can always be issues when altering buildings from their original construction but you really need to balance these with the positives of doing such work.

For years I have surveyed properties with unfilled cavities which are due to be filled and the same issue comes up about a building being able to breathe & I have seen issue where mechanical extraction has had to be added due to condensation issues within the property but this is a tiny percentage of millions of homes which have benefited from being warmer.

It is exactly the same issue with EWI there will always be problems but the vast of homes will suffer no issues and have lower bills and more comfortable homes.

It's a bit like flying yes there is a risk of it crashing but we still fly as the risk is very low.

Smiley_Dan

Thanks for your post Dave. We should always be judicious, of course, when installing such fundamental updates to the building fabric. The same thing applies to CWI; if you are on the west coast or an exposed location, for which cavities were invented, it might not be the best thing to do.

Some more reading: http://www.boards.ie/vbulletin/showthread.php?t=2056166150 which brings up some interesting points including how well damage is withstood. It should be noted this refers to Ireland which has a gustier climate. Again, it's about weighing up the pros and cons.

All that said, in most cases it's an excellent thing to do. Those with cavity walls should also not think this only applies to solid wall houses - they can reduce their energy loss through this method. Many cavity walled houses have cavities too narrow to provide sufficient insulation by modern standards. Furthermore, the addition of EWI with a membrane also takes air tightness to a new level, allowing the fitting of "proper" ventilation (not trickle vents or extractor "hole in wall" fans).

Robwiz

External wall insulation is a more elegant solution then internal for a number of reasons: no/fewer gaps in the insulation (floor ceiling voids often get missed on IWI retrofits) and the thermal mass of the building is on the inside to retain heat.

Breathability (more accurately vapour permeability) is important. If a building is vapour permeable (lime mortar and plaster in the construction) then natural insulation materials (e.g. wood fibre or cork) and a lime mortar render should be used for either EWI or IWI.

The big risk is the contractor isn't knowledgable enough and uses inappropriate materials.

Djwuk

Robwiz wrote: »

External wall insulation is a more elegant solution then internal for a number of reasons: no/fewer gaps in the insulation (floor ceiling voids often get missed on IWI retrofits) and the thermal mass of the building is on the inside to retain heat.

Breathability (more accurately vapour permeability) is important. If a building is vapour permeable (lime mortar and plaster in the construction) then natural insulation materials (e.g. wood fibre or cork) and a lime mortar render should be used for either EWI or IWI.

The big risk is the contractor isn't knowledgable enough and uses inappropriate materials.

Fully agree. Unfortunately from the contractors I spoke to, who were authorised by the Goverment scheme, all wanted to use the latest fancy render systems which did not include the natural insulation materials you mention. Thus reason for my post.

Actually since winter has kicked in, I'm pleasantly surprised the house is relatively easy to heat. From some building work on the house I have noticed the lime plaster has been applied pretty thick on the walls, so I assume this helps insulate the walls . I don't think the payback period on EWI or IWI is worth it for me personally, but could be different for others.

Smiley_Dan

The other thing is that methods for application can differ. Some systems suggest not applying below the DPC, but many architects and building physicists insist this loses much of the benefit.

This, in addition to the detail that is just glossed over on a lot of GD installs. For instance, what to do about the eaves, and the continuation of the insulation over the roof or at least over the cavities, joining the loft insulation. Many GD-ealers appear to just put those caps on the top of the insulation, leaving big scope for thermal bypass.

Also, EWI onto window frames is important.

Anecdotally, it seems the GD-ealers want to get it done and move on...