EWI options for retrofit

[T J Holt]

I am currently considering EWI for my solid wall 1950s brick detached house. (The overall plan is to aim for a high standard refurb, probably falling short of EnerPHit). The likely options, unless someone has a better suggestion, are:

a) 150mm boards of Phenolic and mechanical fixings as necessary (which can't be recessed into Phenolic)
b) 165mm boards of PIR and mechanical fixings (which can be recessed into the insulation and covered with a plug of insulation).

– Of these two options, I'm guessing the u values will be pretty similar – is that correct?
– Is one option more “user friendly” than the other in terms of cutting to fit around windows etc.? (I envisage that our triple glazed windows will be installed proud of the brick wall so that they sit within the insulation, and are also overlapped by it on the outside).
– On the square bay we have been obliged by the planners to have a brick slip finish. Do options a and b above perform equally well with the extra weight of brick slips?

Many thanks,
Tina

[Anonymous]

If option a and b achieve a similar U value , then I guess costs could be used as a deciding factor.
thicker insulation create problems with detailing , but at your thickness there's not a lot in it between the 2
Get the supplier to do the calcs. to compare performance .
Not tried the sunken fixing method , but I have notice on jobs with the thermal break fixings, on a cold frosty morning you can see a very slight outline of the fixing created by the dew , as I presume its acting as a thermal bridge and causing water to condense above the fixing

cheers Jim

[T J Holt]

Thanks Jim. I've heard about being able to “see” the fixings in certain weather conditions, but have no idea whether this a problem or not.

I wonder if anyone knows if this would have a significant negative impact on the thermal performance of the system or if there are any other long term effects (with PIR or Phenolic)?

Regards
Tina

[Anonymous]

The type of fixings should be taken into account when the supplier/designer does the U calcs.
I'm not an expert but I'd have thought the board would be unaffected as the effect i mentioned happen on top of the waterproof render layer , and it is very slight

[Robert Rickey]

I am doing the same research. We recently visited Adam Dadeby's PH refurb in Totnes, where he is using phenolic insulation to keep the thickness down. A stack of boards seemed to show degradation from the sun, and I have heard warnings about phenolic delaminating. I am looking at EPS with graphite, which seems to give a good price to performance ratio. It has the additional feature of being vapour permeable, unlike the extruded products.

[Nick Grant]

Fixings often overdone in UK I believe, on continent they rely more on adhesive.

The visible circles may be thermal or could be thicker render holding more moisture?

Have seen this where board edges get damaged so there is a line of thicker render that shows board shape as darker line even though no gap letting heat through.

Not saying that is happening in case of seeing the fixings but worth having in mind when working out what is going on.

[Anonymous]

I would look into the use of thin coat renders over eps with graphite. With it being such a new product with no performance history I would be wary.

[Author]

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