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Radiant barrier loft insulation

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As the top floor of my house has just climbed above 30 degrees, I'm starting to wonder if some extra insulation might help. There's fibreglass insulation between the ceiling and loft floor, but in the loft there's just some sort of black plastic sheeting which looks to possibly be perforated and then the roof tiles. It gets obscenely hot in the loft.

Is it worth putting some extra insulation under the roof? Had a bit of a Google on radiant barriers but have a few questions that I can't seem to find easy answers for. Does it need to be vapour permeable? Should I staple it to the underside of the rafters, leaving an air gap, or should it be right up against the existing plastic lining? Screwfix and Wickes etc sell rolls of what's basically silver coloured bubble wrap, would this be ok or do I need something more specific for the job?

Cheers

In reply to a crap climber:

> As the top floor of my house has just climbed above 30 degrees, I'm starting to wonder if some extra insulation might help. There's fibreglass insulation between the ceiling and loft floor, but in the loft there's just some sort of black plastic sheeting which looks to possibly be perforated and then the roof tiles. It gets obscenely hot in the loft.

> Is it worth putting some extra insulation under the roof? Had a bit of a Google on radiant barriers but have a few questions that I can't seem to find easy answers for. Does it need to be vapour permeable? Should I staple it to the underside of the rafters, leaving an air gap, or should it be right up against the existing plastic lining? Screwfix and Wickes etc sell rolls of what's basically silver coloured bubble wrap, would this be ok or do I need something more specific for the job?

> Cheers

I think you're more likely to keep heat in than out that way (which also might be valid). What you need is ventilation or to stop heat from the rest of your house entering the loft.

In reply to r0x0r.wolfo:

My thinking is that the sun is heating the roof space up (its significantly hotter than the outside air temperature), and this is then warming up the inside of the house.

A better answer might be more insulation between the house and the loft, but this would require raising the hight all the boards in the loft, which isn't necessarily a massive job but not quite the quick win I'm looking for.

In reply to a crap climber:

> My thinking is that the sun is heating the roof space up (its significantly hotter than the outside air temperature), and this is then warming up the inside of the house.

> A better answer might be more insulation between the house and the loft, but this would require raising the hight all the boards in the loft, which isn't necessarily a massive job but not quite the quick win I'm looking for.

How do you get into the loft?

If you touch the tiles, are they hot?

In reply to a crap climber:

Sounds exactly like my loft - wavy tiles with felt underneath. You can just feel the heat radiating into the loft on sunny days from the southern side of the house. I'm going to go down the radiant bubblewrap route I think as I've done kingspan in the roof of my old house garage and it was a pain.

Look up 'cold roofs and warm roofs' - I think the idea is that you need to avoid condensation on the outside of your bubblewrap that'll rot the rafters. That means sealing that void completely to stop moist air getting in at all, or having ventilation to allow any cold damp air to escape. So, simply bubblewrapping to the rafters isn't likely to be airtight enough thus it looks like the only way forward is to leave a gap at top and bottom which is simply going to allow the air heated up in the void to rise into the top of the roof and warm up the loft.

EDIT - I've not read the links yet, but apparently it's not very good? I can do a test next week as I have some kicking around I intend to fit.  Googling for 'how to fit reflective bubblewrap' comes up with plenty of links to how-to pages and general articles about it.

Post edited at 23:34

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