External building insulation.

Sep 15, 2026 Last reply: 1 month ago 6 Replies

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Timatmarford 1 month ago

Could someone kindly point me to a chart giving worked examples of using exterior foam insulation materials?

I have skimmed through John's house cladding job in the Wiki.

The tenancy of my old pig fattening shed (now Robot Centre!) has changed to the Son on a new agreement. I suspect this will alert the local authority and trigger interest in current E values:-(

Solid floor, single story, rendered blockwork walls, double skin steel roof including 100mm foam insulation. Too many wall mounted fittings to consider internal work.

Gutter overhang not huge but I might get 100mm on, finished with feather edge boarding to match neighbouring structures.

An upside is that the introduced internal moisture is limited to breathing and their kettle:-)

Tim

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Information here may be outdated?

Theo 1 month ago

I don't have a chart, but

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allows you to experiment with different material stackups and tells you the U values as well as condensation, drying time, heat capacity and heat transfer delay.

Use it in demo mode unless you want to save the results, or want access to branded materials. The standard materials are a bit lacking in places - eg use PUR instead of PIR board.

The key to getting something good is in the detailing. It's easy to forget about how eg walls and roof interface, which can lead to poor performance like draughts or cold bridges. Also you need to ensure that there is sufficient drying potential, otherwise you may have moisture retention and eventually rot.

Theo

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Timatmarford 1 month ago

OK Theo. I'll have a look. The building occupation is sporadic in that the bulk space is rarely occupied: with fan heaters used for the office areas and the remainder storage. Sadly I doubt District Council E value consultants will accept that.

Tim

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John Rumm 1 month ago

Worth noting that the introduction of tightened EPC rules on rented accommodation have been delayed to Oct 2030 now.

There are some figures and typical u/k values here:

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For retrofit internal or external wall insulation, you are looking for

0.30 W/m^2K or better. (there is an exception that allows that to rise to 0.7 W/m^2K in worst case situations where you can't feasibly hit the preferred target). [1]

Not sure what type of block you have (a heavy concrete one has *very* poor insulating properties - and a thermal block not bad), but if you can get at least 80 mm of PIR foam on top, then it does not matter much since the insulation alone will meet the target.

[1] See table 4.3

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(I probably aught to add that to the wiki page)

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Timatmarford 1 month ago

Would that apply to a commercial workshop?>

Hmm. Cheapest possible blocks available in 1960! Certainly concrete and unlikely to have thermal voids.>

My brain hurts. They seem pretty adamant about using professional designers.>

Thanks John. I should have looked more closely before bleating for help!>

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John Rumm 1 month ago

From a quick search, the rules for letting commercial space are different (and also depend on the size of the property). I believe you need a EPC grade E or better at the mo. There is an exemption that can be applied for that allows F & G rated building to be let if you can demonstrate the payback on the cost of insulation is longer than 7 years.

Cinder block was common then... probably comparable to a modern medium strength block (thermals a bit better than protected brick)

Yeah, I skip over those bits :-)

(I did add another section about "how much" insulation to use)

Its good to talk as they say :-)

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