Rafter Insulation — Remove or Keep?

thegreenone

laurencewhymark said:

Thanks thegreenone!

Do you know why water was making its way in occasionally? Was it lifted tiles, or during heavy winds water was finding it’s way upward?

Apologies for not replying sooner.  We think the rain was just blown in, as it wasn't a lot. Fingers crossed yours is the same.

Bendy_House

You are welcome - but don't come crying to me if your ceiling falls in.

Only kidding!

paperclap

Here’s to praying we survive the winter! 

paperclap

twopenny said:

Once sorted lay some new insulation to standard remembering to leave a gap near the eves for ventilation.

After I’ve found and sorted any potential leaks, you’re suggesting having the rafters insulated again?

This current polystyrene and plasterboard already had the (minimum) 50mm ventilation gap from top to bottom. With this insulation, we don’t have condensation issues. Only rainwater leaks. My concern was that if I were to remove the insulation, I would actually get condensation, because of the larger thermal bridge!

But I’m getting the general consensus (in this thread) that any insulation, even with a ventilation gap, is just a bad idea between rafters?

BikingBud

If considering a loft conversion in the future is there any value in replacing the rafters with SIPS and thereby giving the necessary headroom and clear run? Get a well insulated space that provides at the minimum good dry and insulated storage.

Boarding of floor can come after and fitting out, skylights, room organisation, electrical/plumbing fit etc when time and funds allow.

FreeBear

laurencewhymark said: But I’m getting the general consensus (in this thread) that any insulation, even with a ventilation gap, is just a bad idea between rafters?

Insulating a heated space is good (the more, the better). Lofts are (generally) unheated, so there is little point in insulating between the rafters. Put insulation down between the joists to keep the heat in the rooms below. Condensation within the loft space shouldn't be an issue as long as there is sufficient ventilation.

If/when you convert the loft in to a habitable space (and heat it), then you would need to insulate between the rafters, along with a bunch of other work to comply with building regulations.

Bendy_House

laurencewhymark said:

twopenny said:

Once sorted lay some new insulation to standard remembering to leave a gap near the eves for ventilation.

After I’ve found and sorted any potential leaks, you’re suggesting having the rafters insulated again?

This current polystyrene and plasterboard already had the (minimum) 50mm ventilation gap from top to bottom. With this insulation, we don’t have condensation issues. Only rainwater leaks. My concern was that if I were to remove the insulation, I would actually get condensation, because of the larger thermal bridge!

But I’m getting the general consensus (in this thread) that any insulation, even with a ventilation gap, is just a bad idea between rafters?

I understand 2penny was referring to the ceiling joists, not the roof rafters.

If the stuff on your rafters had the important 2" ventilated gap above it, then - in theory - there wouldn't be any condensation building up between it and the roof covering which could lead to timber rot. At least not if this gap was ventilated properly in its own right.

But, the main loft space under that insulation/p'board layer would also need to be fully ventilated - via the eaves, for example, if you were to prevent any condensation forming in there.

So, with both sides of these sheets being 'fully ventilated' - as they should be - the 'insulation layer' there would have served no purpose.

I suspect it was put there by the homeowner, in the mistaken belief that it would keep the loft warm and dry. It might have kept the loft area slightly more warm as long as the loft wasn't ventilated. But if the loft area wasn't ventilated (which would make it cold again) then you would have condensation (so it wouldn't be dry) forming up there - just as you would in any cold, unheated and unventilated room in your house. And you know about that :-)

The only way to make that loft warm and dry is to separate - 'seal' - it from the roof rafters with a barrier of insulation (which is fully ventilated above it to the eaves) and then to add both heating and a controlled level of ventilation to that loft space, say by having opening windows and/or trickle vents.

Ie - by turning it into a proper loft room.

paperclap

Thanks all! I had misunderstood that previous post regarding the rafters/joists.

You're quite right, Bendy_House. Without controlled heating (e.g. a radiator) it is almost useless having insulation there.

Let’s say hypothetically that there were no leaks (or “hidden” leaks). Would there be such a use in removing it all? From my understanding, it has been installed correctly, as it does have the required ventilation gap sitting between the tiles and insulation.

Bendy_House

laurencewhymark said:

Thanks all! I had misunderstood that previous post regarding the rafters/joists.

You're quite right, Bendy_House. Without controlled heating (e.g. a radiator) it is almost useless having insulation there.

Let’s say hypothetically that there were no leaks (or “hidden” leaks). Would there be such a use in removing it all? From my understanding, it has been installed correctly, as it does have the required ventilation gap sitting between the tiles and insulation.

I wasn't originally aware that it had the necessary 50mm+ ventilation gap above it, so provided this gap is open to the general loft space (and eaves) so that it is well ventilated, then I can see no necessary reason to remove it all. So, everything you've taken out, you can put it back now... :-)

I personally wouldn't, tho' - it serves no purpose (unless you are hoping it'll catch incoming rain...) and does run the risk of reducing ventilation against these rafters. My concern is that I suspect it wasn't fitted by someone who necessarily knew what they were doing, so if it's actually fitted 'correctly' (tho' ineffectually), that's just good luck. Bear in mind that the 50mm+ ventilation gap should still have a felt layer between it and the slates so no rain gets to the insulation.

If you are confident that there's a good gap above it, that this gap is well ventilated, and that there's no sign of damp patches on the rafters, then by all means leave it and monitor it :-)

There's no reason for your slates to let in rain, unless there's some unusual weather conditions - eg a strong blustery wind and heavy rain. If it does, then that's the purpose of the secondary 'felt' layer. However, since you don't have this secondary layer - or it's seriously compromised - then you need to consider where any rain could end up instead. The most likely place is on this insulation, which means in the tight butted gap between the insulation sheets and the rafters. That is what you don't want.
I don't want to over-egg this - chances are, from what you've described, that there will be no issues at all. But I'm just pointing out that (a) the insulation serves no purpose, and (b) it could possibly cause issues.

paperclap

Thanks again for showing me the light, Bendy_House! And I don’t mean the light through my tiles! 

You’re right, it actually serves no purpose and has no benefit. The space isn’t heated, and it isn’t a habitable space.

As you say, it could however cause big issues, if that rain water does find it’s way in. It could run down the insulation and pool in the eaves. Or, worse, collect around the timbers, and take forever to dry (and there is less ventilation).

If there is a weak spot (perhaps a larger gap than usual) somewhere. I not only want to know about it… but would much prefer it to drop directly down, rather than anywhere else!

I know I’m sort of reiterating what you’ve already said, but I’m just telling myself I’m doing the right thing in removing it all! 

It is an absolute horrible job to do. Incredibly messy. Pain in the !!!!!! storing all the insulation and plasterboard. Takes forever to do, especially when I’m doing it myself, the screws are in deep, and I’m balancing on joists. Only done about a quarter so far!  

We have had wet timbers (a purlin, joists, battens), all in different places, and some of those areas were never rectified as such. I couldn’t see gaps externally (on the tiles). And frankly, who knows what other areas have been wet in the past!

I think in all honestly, it does just need to come down. All of it. Not just areas where I know it’s leaked.