Warm Roof/ Cold roof choices…

[Alexander Ward]

My immediate concern with that system would be what the U-Value is where it laps with battens and gets compressed. If the u-values tank when the layers of the multifoil are squashed together then you’ll get cold bridging into the roof timbres which would then be liable to having moisture in the air condense on them.

How much of a problem would that be in practice? Who knows. And thats the issue with new methods and new products.

Can I ask why you want a warm room? Is it so you can use the attic space?

[Brian Taylor]

I think you need to read more on the topic.

A warm roof prevents condensation because the air below the final layers of roof is kept warm, and there is a barrier to prevent this warm moist air getting into the final layers of the roof.

A cold roof concept accepts that cold air could be in contact with the final layers of the roof, because there is a gap between the upper/outer surface of the installation, and the bottom of the actual roof. It therefore has ventilation requirements.

This reduces condensation because the air is kept moving.

i would also highlight, that ceilings of houses need to be vapour proof (i.e. airtight) on the warm side of the insulation.

With everyone trying to make loft spaces colder, condensation becomes more and more of a problem, so reducing the ability for vapour to get into the cold space is key. Simply adding insulation results in there still being an amount of vapour that comes up into the loft to condense, or make the top layer of insulation wet (from it condensing at the top layer of insulation)

[Alexander Ward]

exactly. The keeping the loft space warm is the old way they used to do it with little insulation above the ceiling. A method that works well for condensation but doesn’t do a lot for the energy bills.

Increasing air flow tends to be a ‘treat the symptoms’ approach, where minimizing it getting up there in the first place, together with a little air flow achieves what is probably a better result.

[Brian Taylor]

agreed. Although at the end of the day though, if the entire roof space is kept warm, moisture isn’t such a problem.

If there aren’t any cold surfaces for the moisture to condense on, it remains in vapour phase. Almost all solutions to condensation focus on keeping the moisture where the warmth is.

If you can’t, you have to make sure the air is moving quickly enough, to take the moisture outside with it.

[Charles Brown]

TLX Gold is a magic insulation product that gets a hard sell from roofers. I have seen it used numerous times and it is always useless due to poor thermal properties and thermal bypass from cold air passing around it at the roof eaves junction. Thermal imaging and a door blower test shows just how bad it can be. If you want a warm roof look at the Historic England document attached above and look at products like woodfibre, but understand the increased loading it will put on the structure. If you are not using the warm roof space in the loft as habitable space just stick to a cold roof space. Cheaper and easier to get right.

[Marcus Robson]

Check also if the material is suitable for bats, if not then you will probably need to use bitumastic underlay.

The Bat Conservation Trust has a very good website.

Most claims for underlay sound good, but over time debris and dirt will clog the material and reduce the breathability.

Query if the builder is experienced with older roofs.

[Neil Andrews]

Warm & cold roof generally applies to flat roofs, however the principles can be applied to pitched roof.

There is absolutely no need & no benefit whatsoever to insulating a non inhabited area. You are litterally throwing money away.

Ensure you have very good (300mm) loft insulation throughout the loft space whilst ensuring the insulation does NOT touch the roof membrane and a good passage of airflow is maintained. Worth ensuring you have a good tight seal around the loft hatch too preventing the warm moist air below condensing in the loft space.

[Jay Hucklesby]

thanks, yes I know felt goes under the battens, it wasn’t my intention to do that on the tiled part of the roof. However there is the untitled part (adjoining the loft) where I was considering what insulation to use there. It’s also unattended, just simply rafters with plasterboard and plaster between the joists.

[Peter Robinson]

My only comment in situations like this is why are considering a warm roof system unless you are looking to utilise the roof space as an occupied room.

If you are solely looking to upgrade the thermal efficiency of your property at the roof line then loft roll insulation will keep the thermal line at the ceiling joists. If you insulate at the rafter line all your heat will spread into the loft space rendering it wasted heat.

Unless I have gotten the wrong idea here you should insulate at the ceiling line for existing roofs unless converting the roof.

[Rich Murray]

I had a so called reputable company, “experts in heritage roofing” replace my roof and they used this. They botched the job completely, took years and its an absolute mess. In the end they installed about 20 vents because they realised its not breathable and will eventually rot everything. They’ve since gone into administration. Looks like they’ve set up a new business though. I can tell you who to avoid in yorkshire/the north west! We’ve had to replace some of the vents due to leaks, even though they did actually appear to be installed correctly. But our attic is now freezing cold, little bit leaky and rotting.

[Ron Johnston]

Here we go again.

There’s a difference between warm roof/cold roof and warm roof space/cold roof space.

I think you are referring to the latter.

You can have a warm roof space but a cold roof.

If the insulation is underneath or in-between the rafters with a ventilated cold space between the tiles and the rafters that is a cold roof.

If the insulation is completely above the rafters that is a warm roof.

Both will give you a warm roof space.

If you insulate on top of the ceiling joists that is a cold roof space.

All are fine if done correctly.

All are terrible if done incorrectly.

A cold roof is the one that is hardest to get right and most commonly ballsed up.

[Jay Hucklesby]

here we go again? Not sure what you mean. Is this question coming up a lot about TLX Gold?

Yes we are talking warm roof space vs cold roof space, I don’t think there are many people here looking for a warm roof with a cold roof space.

If you have any feedback on TLX Gold would be great though.

[Ron Johnston]

you’ve still not understood what I said. People regularly confuse the terms hence my comment, you clearly still are

You are not talking about warm roof Vs cold roof.

You are talking about warm roof space vs cold roof space.

I’m not saying it to be pedantic I’m saying it because if you talk to people or research online asking about warm and cold roof you will get completely the wrong answers.

[Simon Henderson]

Following as our roofers are also suggesting TLX gold and am interested to hear experiences of it.

[Steve Philips]

What a surprise, another roofer wanting to use TLX gold. Kickbacks are great.

[Simon Henderson]

it’s not the case here. I have been doing my own research.