Wall wrap for brick veneer

I found that our builder doesn't include any wall wrap as standard, but in asking for them to quote for it, there's the simple question of which product to use?

Maybe it's not worth getting at all, but I figure the advantage is as a moisture barrier, and to help the insulation work better by restricting air flow, protecting against contact with the brick, plus some reflective insulation. Perhaps it isn't so important here in Adelaide, as the air is generally dry, and perhaps less need for a moisture barrier?

The thing I find odd is to do with the reflectivity of the wall-wrap. It looks like most wall wrap products are single-sided reflective, with the reflective side on the inside. With the R2.5 of insulation in the walls, I believe that reflectivity is pretty useless as there is no air gap on the inside, but rather you want the reflectivity outwards to the cavity. There are some double-sided reflective products around, with one bright, and one dull side, but these don't seem geared to wall wrapping.

So given that everyone is filling walls with batts now, what is a suitable wall-wrap to use with brick veneer? I'm guessing an anti-glare reflective surface on the outside, with emittance of 0.05 or less, and appropriate vapour and water barrier properties. Where do I find such a thing?

After more digging around the manufacturers' websites, I think I'm starting to get a bit of sense out of it. Oddly though, most products don't seem to suit the most common application of brick veneer with insulated stud wall. On their websites it's often hard to find which products actually have an outward-facing foil.

In Bradford, their product looks like Thermoseal Wall Wrap XP, which is the only model I can find with an outward-facing reflective surface designed for this purpose. It is non-permeable through, and Bradford recommend permeable wrap for R2.0 insulation and higher.

In the Sisalation product range, the products marketed as a wall wrap all appear to be reflective on the inside only. However, the multi-purpose light duty 439 product is a double-sided foil (anti-glare on outside), but non-permeable.

The Ametalin SilverSark xR is also double-sided, and advertises "Advanced condensation and moisture control" - but the data seems to give no indication of what that actually means. The water vapour barrier classification is "medium", but I'm not sure if the permeability is high enough to avoid condensation problems in this application. It has one of the higher specced reflective performance on the anti-glare side.

At the moment I'm leaning towards the James Hardie HardieWrap weather barrier. This is reflective on the outside and also permeable. The reflective insulative benefit is probably not as high as some of the others (0.16 emittance, vs 0.05 emittance of SilverSark xR), but I'm thinking it may be worth trading off to get the higher permeability.

Hey Mate I have been wondering the same. We are also building in Adelaide and I was going to do the Western wall only in a foil wrap. I'm going to do it myself when the builders are off site. All sites seem to indicate foil facing the inside? However I only want to reflect the radiant heat back out from the hot afternoon low sun in summer. We are spending an extra 4K on sisalation to the roof to avoid the condesation, but I gather this does little for heat sheilding as the foil face's in?

Foil works both ways, in that a reflective surface will reflect radiant heat away, but also that if a reflective material is hot, it won't tend to emit radiant heat. It acts as a heat barrier in both directions, but the important thing is that the foil is facing an air gap of at least 20mm or so for it to be effective.

So for roof sarking, the foil facing down is the right thing to have. As the foil heats up, it tends not to transmit that heat by radiation down into the roof. Upward facing foil isn't generally so good, as it gets covered in dust, and then the dust defeats the action of the foil. The best thing for a metal roof are products like bradford anticon, which have foil facing down, and then an insulating blacket between it and the roof sheets.

With walls, when you have the framing void filled with insulation, a foil on the inside doesn't have much benefit, because it is touching the insulation, and then conducted heat is more important than radiated heat. So inward foil isn't suited in combination with batts. You can get outward facing foil, and double-sided foil sarking, though in these cases in doesn't look as mirror-like as it will be anti-glare treated to prevent glare problems during construction.

If you're putting the sarking on by yourself, just watch that it does affect the work of the bricklayers. They may need to use different brick ties, and it gives them less access.

Cheers John, some great info there. Cleared a couple of things up for me. Good point with the brickies. Most of the large volume builders here in Adelaide seem to use a wrap on the external walls to keep the work moving on the inside so may be ok.