What type of insulation to use for steel cavity lintel externally?

[MikeGrahamT21]

Bought a new thermal camera the other week, and have since found a number of 'defects', or rather things i didn't realise would have been such an issue.

 

I have 4 openings which have IG Cavity Steel lintels, non thermally broken, but they are insulated in between the cavity with polystyrene. It seems that now i'm well on my way to insulating everything in sight, this has become a much more obvious point of heat leak than it was before. The steel of the lintel is visible externally, I was going to glue some PVC trims to match the windows but never got round to it.

 

I'm now thinking to use some form of insulation, and then make a box section out of PVC trims to hide that insulation, but what to use? It would have to be fairly thin, and i had a quick look at Aerogel Thermal Bridging Strips, but having never used it before not sure how well it would work in this scenario, and even it it would be suitable to be used externally (1 of the lintels is well hidden away from the elements, but the others are exposed).

 

Other options are neoprene which i've got a part roll of, much like the aerogel strips its adhesive backed to stick to lintel, and should be fine to stick other things to it, in terms of the trim.

 

What would you use for this purpose?

[MikeGrahamT21]

Spent a bit of time looking at different options today, aside from whats mentioned above, rigid insulation board, which has brought these options:

 

• Bosig Phonotherm 200 (1.35m x 500mm x 15mm)  - 550kg/m3 density and 0.083 W/mK conductivity - £43.20 per length - Delivery at £65 makes it uneconomical though
• CompacFoam (0.97m x 100mm x 20mm) - 200kg/m3 density and 0.046 W/mK conductivity - £13.64 per length - Delivery at £25
• BRIGi Foam (1.2m x 100mm x 20mm) - 150kg/m3 density and 0.040 W/mK conductivity - £12.57 per length - Free Delivery

 

The Bosig just doesn't make sense, poorer thermal values and a lot lot more expensive. So that leaves CompacFoam and BRIGi Foam, which are both flame retardant EPS products. And the cheapest one of those is the best in terms of conductivity.

 

Hadn't heard of BRIGi foam before today, but its read up suggests its an ideal product.