Does loft boarding cause condensation beneath?

[PaulUszak]

I'm thinking of boarding my loft, and have seen loft feet /spacers in the DIY stores. They raise the joist level 170mm. With an existing 100mm joist, that would be 270mm in total. This is coincidentally the current recommended insulation thickness. If you go with the recommendation, insulation will fill the entire void beneath the loft boards, and touch the underside of them.

This arrangement can be seen on the Wickes website for the Loftleg. The chap's insulation there is level with the top of the Loftlegs.

Is there a risk of condensation beneath the boards as there will be no gap between the boards and the insulation?

PS. I've just asked same of the founder of Loft Leg Ltd. He says that there will be a token amount of condensation accumulating throughout winter. This will then evaporate during the summer months. In short, no condensation. He cited proof by Lancaster University. I cited Star Wars. Does this seem credible, and is there any conflicting evidence?

 

[Instaloft]

You should leave a 50mm air gap between the insulation and the boards to allow adequate ventilation.

We tested loft legs and found them unsuitable but many people do use them. You would be better off using Loftzone which has been thoroughly tested and approved by the BBA for boarding insulated lofts.

 

[PaulUszak]

You should leave a 50mm air gap

Do you have any substantive evidence for this, or are you just dissing Loftleg because you're a competitor installing the more expensive product? [I read your recent posts]

I'm not connected to the trade and agnostic in terms of systems, but I am attuned to marketing hype

 

[Instaloft]

I'm not marketing at all or offering. This is a DIY forum.

I have tested both and found the loft legs were not in my opinion physically substantial enough. Not just from a personal point of view but naturally as they were cheaper we looked at them as an alternative. I didn't want to risk installing them based on my own tests. This was from a strength point of view rather than the fact that they don't leave the air gap.

I suggested a solution to your issue that I know works well. The BBA test many building products over a long period and only approve those that meet very strict requirements. The Loftzone system was approved for boarding insulated lofts. I can provide the link to the BBA website if you want but I don't have access to all the tests etc.

I think I have a link to the air gap somewhere and will try and dig it out. Like many things it's subjective. Some people will tell you to use timber to raise the boards over the insulation instead. Personally I wouldn't for the same reasons you are asking about.

As a business we have "reboarded" countless lofts and after removing boards that have been installed directly onto insulation have often found them (not always I'll add) to have mould growth, damp patches/signs underneath etc. So just from experience I offer the same solution that we use in those situations. I don't benefit from you buying from Loftzone as I'm not part of the manufacturer.