mdroyle

Exterior Wall Insulation - advice re options

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House is a 1970s box. Has hanging tiles on half of first floor. House generally feels colder than previous house. So, looking to improve heat retention.

 

I got a cost to remove existing cavity wall insulation and replace with blown bead  but actually I think spending the money on exterior wall insulation would be better as also want to remove hanging tiles and render the whole house anyway.

 

Any thoughts / guidance / experiences on best materials for exterior insulation and render very welcome!

 

 

Mike  

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It is a good idea if you are detached.  You need to consider the soffit overhangs, windows reveals, soil pipe positions and anything you are planning to fix to the outside.  I have seen it done with EPS and with PIR.  I think EPS would be my choice.  They use adhesive plus a few mechanical fixings for each board, then thin coat render with a mesh coat.  You should try to get floor insulation done at the same time.  All fairly disruptive.

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If going the external insulation you've different levels that you can go to. Obviously the more you do the better the job. These apply to detached, semi detached and terrace. 

  • If you take out the footpaths around the base of the house this will allow the external insulation to continue underground say 300mm or more if possible.
  • Removing the fascia and soffit will allow you to continue the external insulation up further between the timber rafters and connect with the attic roof insulation eliminating any cold bridge. Leave just enough of a gap to ventilate the attic if you've a cold roof buildup.
  • Replacing the windows at the same time as external insulation allows you to move the windows out so they're in the line of the insulation. You'll have deeper reveals internally which is better than the deeper reveals externally which will be a cold bridge. This looks a lot better too as avoid old looking windows with a new fresh rendered house.
  • If you externally insulate you still need to pump the remaining cavity of the wall to prevent thermal looping.
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Very interesting folks and thank you for your replies. I am looking to do something with floor insulation as we'll be having new floor coverings on the ground floor - but not prepared to dig out existing solid floor and don't want to raise the floor much - so was looking at warmup boards which i think are 6mm - maybe I could go a little thicker though.

 

The point re going underground externally by 300mm is interesting - in reality how much difference will this make as clearly there is a cost to dig out.

 

Also please can you explain what you mean by pumping out the wall cavity to prevent thermal looping?!

 

Thanks, Mike

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11 minutes ago, mdroyle said:

Very interesting folks and thank you for your replies. I am looking to do something with floor insulation as we'll be having new floor coverings on the ground floor - but not prepared to dig out existing solid floor and don't want to raise the floor much - so was looking at warmup boards which i think are 6mm - maybe I could go a little thicker though.

 

The point re going underground externally by 300mm is interesting - in reality how much difference will this make as clearly there is a cost to dig out.

 

Also please can you explain what you mean by pumping out the wall cavity to prevent thermal looping?!

 

Thanks, Mike

In the cavity if you've it half filled with insulation you still have air which can circulate and move about. Old houses have draughts and it's possible for the cold air outside to get into the cavity, eg at the roof, and circulate in the air cavity in the wall. It's basically bypassing the external insulation. If the cavity is fully filled this can't happen. 

 

As for continuing the insulation underground externally this is useful particularly where you're not able to replace or insulate the existing floor. It's not perfect but does help. If you are moving a lot of rain water pipes you might be having to take up parts of the footpath anyway. Obviously if you've tiles in a patio or expensive paving instead of a gravel path or cheap standard concrete this option of continuing the insulation underground becomes more expensive. It is a relatively easy DIY job so breaking out part of the footpath and digging the trench is something you can do yourself to save money. I did it on my house.

 

If you go for 100mm of external insulation or 150mm or 200mm the different in cost isn't massive as the main costs are in the labor, scaffolding hire, plastering, moving rainwater pipes, etc which are needed for each. The additional cost of insulation thickness isn't a lot and well worth adding as much as you can. If you're going to the effort of temporarily removing the fascia and soffit to continue the insulation up to the roof you should have nothing stopping you going for 200mm in thickness for example.

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The EWI gets complicated quickly, if you're doing it right.

 

  • Avoid caps at the top of the insulation e.g. at gable verges and extend the roof line instead.
  • You might have to move drains.
  • You might have to move meters.
  • You'll have to extend any penetrations.
  • Extend the insulation through the roof at any lean-tos to meet the insulation there (depends on cold/warm roof).
  • Consider using higher performance insulation (e.g. aerogel) at the reveals.
  • Ideally go further than 300mm underground, foundations permitting.

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+1 to @gravelld comments. Easy to do badly, can be very tricky to do right

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There may be grants available for external insulation, so look for that also.  Could save a bundle of cash.  My wife sister recently had it done cost zero.

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4 minutes ago, JohnMo said:

There may be grants available for external insulation, so look for that also.  Could save a bundle of cash.  My wife sister recently had it done cost zero.

The grant done work is often worse than not having any. Poorly fitted, water getting behind, cold air gaps and horrible work and detail around window and door reveals

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1 hour ago, markc said:

The grant done work is often worse than not having any. Poorly fitted, water getting behind, cold air gaps and horrible work and detail around window and door reveals

Nonsense. That can happen on any project and is down to getting a good contractor and supervision onsite. 

 

I got the grant for external insulation in Ireland but it's probably different elsewhere. Here you've to pick from a list of approved contractors who are registered for the grant process. The work has to be signed off and any issues you can go to SEAI (Sustainable Energy Authority Of Ireland) who oversee the grant process. We had one wall we didn't think was great quality and they came back and redid it. If they don't reach a certain standard they risk getting removed from the list of approved contractors.

I know several projects where the SEAI made them come back and do additional or rectification work. The problem in Ireland is the oversight, sign off and additional paperwork involved pushes up the contractors cost which they have to factor into their costs. This means if the grant covers eg 50% you're probably getting a 40% saving on doing it yourself without the grant.

 

The advantage is you've great power in getting them to come back and fix issues which would be incredibly difficult on a non grant project. On a regular non grant job If the builder is finished and paid its very hard to get them back to fix something. One example on a project I was working on is the external render was black. Natural salts came out and left patches of white like you often see on new brickwork. You only noticed it as the render was black. They were made come back 18 months later after all the salts, calcium or whatever it is had come out and acid wash the elevations for free. Good luck getting that done on another project.

 

As I said this is in Ireland and not sure how it works elsewhere.

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That’s why you keep a retention back and pay after a set defect period such as 12 months.

 

if part of the build has plants, sedum we ask for 24 months defect period on these items to ensure we can see growth.

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If I can add an additional point... There is an external chimney made of stone which will be unused when we remove the gas fire. I think it would be expensive to remove, so what's the best way of preventing the chimney being a route for cold air... Could I treat it as a cavity a d fill with say blown beads and seal it off, or could this lead to damp problems, in which case if I have to keep it ventilated I guess there is little to be done apart from love with it?

 

 

Thanks again everyone for your help.

 

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Vermiculite is the common suggestion up to the thermal envelope. Ventilate with a vent at top and bottom of non filled space.

 

If it's being enveloped in EWI could you consider removing the top down to the level of the thermal envelope e.g. first floor ceiling if cold roof,then sealing that in? Then,no need to fill and the space might become a useful service cavity e.g. for ducting.

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8 hours ago, gravelld said:

Vermiculite is the common suggestion up to the thermal envelope.

It is, although I'd choose expanded glass beads as they don't absorb moisture.

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