Green Building Forum - Help please! Condensation in newly converted barn. MVHR vs dehumidifier? Tue, 19 Dec 2023 08:24:48 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286121#Comment_286121 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286121#Comment_286121 Thu, 07 Jan 2021 17:50:25 +0000 chrisduncan Posted By: GreenPaddy You could add a remote humidistat to the existing fan, maybe something like this...
https://crwltd.co.uk/extractor-fan-inline-bathroom-run-on-timer--humidity-sensor-switch-socket-2335-p.asp?


Fantastic! - I will explore this avenue.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286122#Comment_286122 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286122#Comment_286122 Thu, 07 Jan 2021 17:53:48 +0000 chrisduncan Posted By: GreenPaddy What is it you're trying to control? RH in the bathroom, at the window...You might want to be able to de-activated it so it can't come on at night, as say room temp falls, and RH rises. I think I might just put a timer on it, and be done with it. Increase the time period if you see a bit more cond. Off between 10pm and 7am, or what ever.

The minimum is to prevent condensation in the main room where the bifold cill meets the wooden floor. This is about 12m away from the extractor fan at the opposite end of the barn.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286123#Comment_286123 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286123#Comment_286123 Thu, 07 Jan 2021 17:57:06 +0000 chrisduncan Posted By: GreenPaddy That doesn't really help with the main thrust of your question - how to not repeat this in the house.

Now I know the condensation is just caused by people occupying the barn, I can be confident that the new house will be fine with MVHR and the same windows (and see below).]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286124#Comment_286124 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286124#Comment_286124 Thu, 07 Jan 2021 18:14:30 +0000 chrisduncan Posted By: GreenPaddy As others have said, you have a cold bridge at the foot of the window. It may be resting on the metal cill, and bridging the cavity. So metal cill from inside to out, and possibly cold air directly underneath from cavity. Is the cill thermally broken? Is the unit sitting on insulation? Door thresholds and floor based window cill details are often a problem.

Bifold frame sits on 36mm plywood packers on top of concrete blocks. It didn't occur to me that I might be creating a cold bridge by doing so. The plywood supports both front and back of the cill so bridges the thermal break. Arghh.

Well at least I know what not to do in the main house!. I think I might have thought that plywood wasn't enough of a thermal conductor to matter very much.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286140#Comment_286140 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286140#Comment_286140 Fri, 08 Jan 2021 10:32:56 +0000 dickster Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286143#Comment_286143 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286143#Comment_286143 Fri, 08 Jan 2021 15:24:14 +0000 borpin Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286144#Comment_286144 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286144#Comment_286144 Fri, 08 Jan 2021 16:19:30 +0000 chrisduncan
Is Compacfoam 200 still the go-to solution?]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286145#Comment_286145 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286145#Comment_286145 Fri, 08 Jan 2021 17:05:02 +0000 djh Posted By: chrisduncanFor when we get to building the new house I need to know what insulation to put under the cills. I've had a look at some previous discussions on GBF. We will be having sliding doors 2300mm high. Not sure yet if they'll be double or triple glazed.

Is Compacfoam 200 still the go-to solution?
You need to know the weight of the doors and the stated pressure limit of whatever you put underneath, plus any requirements the door manufacturers make for flatness and rigidity (if they require something flatter than whatever you put under it compresses by at working load, you might need something stiffer).

As far as I'm aware Compacfoam is still good stuff. It comes in various stiffnesses, not just 200.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286146#Comment_286146 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286146#Comment_286146 Fri, 08 Jan 2021 18:01:08 +0000 WillInAberdeen
Is that an air leakage path as well as a drainage path?]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286147#Comment_286147 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286147#Comment_286147 Fri, 08 Jan 2021 18:08:26 +0000 djh Posted By: WillInAberdeenIs that an air leakage path as well as a drainage path?
Isn't any drainage path automatically (a fortiori) an air leakage path?

I think the only air seal is inboard,where the sealant is shown to be applied and there's a flexible seal shown above mating against the bottom of the door.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286168#Comment_286168 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286168#Comment_286168 Sat, 09 Jan 2021 16:06:04 +0000 bot de paille Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286278#Comment_286278 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286278#Comment_286278 Wed, 13 Jan 2021 10:54:44 +0000 lineweight
I'm always worrying about the detail under bifolds and in my experience the suppliers/manufacturers are entirely unhelpful in offering any advice on details that avoid a thermal bridge at this location.

In particular, the question of bridging a cavity in a situation where you are building into a cavity wall type buildup. A while back I spent ages trying to find whether there was such thing as a load-bearing cavity closer for this type of situation. My conclusion - there isn't.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16054]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286281#Comment_286281 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286281#Comment_286281 Wed, 13 Jan 2021 11:18:58 +0000 lineweight
So, if you have an insulated cavity, you have to have something that can bridge it structurally. And the materials that can do that tend to have bad insulation values.

But the sill is thermally broken (as per the diagram posted above)... and I might be wrong, but I imagine it is designed such that the load from the sliding tracks is not passed through the thermal break section - in other words, it must be shared by the aluminium bits either side. So potentially you don't actually need structural support directly under the thermal break section.

So, can't it just be designed so that the thermal break in the frame sill can be aligned with the insulation layer in the wall below?

Perhaps it's just not structurally feasible to have an aluminium sill element that can bridge a 100mm or so cavity.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286282#Comment_286282 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286282#Comment_286282 Wed, 13 Jan 2021 11:21:48 +0000 lineweight Posted By: chrisduncan

Bifold frame sits on 36mm plywood packers on top of concrete blocks. It didn't occur to me that I might be creating a cold bridge by doing so. The plywood supports both front and back of the cill so bridges the thermal break. Arghh.

Well at least I know what not to do in the main house!. I think I might have thought that plywood wasn't enough of a thermal conductor to matter very much.
    http:///newforum/extensions/InlineImages/image.php?AttachmentID=7749" alt="bifold cill.png" >


The thermal bridge is likely to be caused by the concrete block directly under the ply, rather than the ply itself no?

In other words there is a path horizontally through the conc block, then once it gets to the inside, you're just relying on the thickness of the ply layer (rather than its depth outside-to-inside).]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286291#Comment_286291 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286291#Comment_286291 Wed, 13 Jan 2021 12:56:57 +0000 djh Posted By: lineweightSo, can't it just be designed so that the thermal break in the frame sill can be aligned with the insulation layer in the wall below?
I think the difficulty with that is:
(a) the thermal break in the frame is actually quite narrow, so there's not much space for insulation, and it's clear in the drawing that the frame needs supporting adjacent to the thermal break, (aerogel maybe?) and
(b) you then have the difficulty of making sure that the two separate structural parts are exactly level with each other and maintain that equality of level over time.

Is one of the Compacfoam products stiff enough to be used underneath a bifold? Or Marmox Thermoblocks or Foamglas Perinsul? And are they strong enough (I guess so, though fixings might be problematic)

When we built, bifolds were regarded as not suitable for PH, so we didn't consider them. I think there are now some PH-certified, so it might be worth asking them for installation details?]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286298#Comment_286298 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286298#Comment_286298 Wed, 13 Jan 2021 14:18:32 +0000 lineweight
(a) I was wondering whether there is a potential design of the frame that would allow a wider thermal break
(b) Yes, I see that in principle, although you could argue this is an issue even if you bridge the leaves further down somehow.

My understanding was that stuff like compacfoam is only strong in compression, not designed to span across gaps, but I might be wrong.

Yes, perhaps I should look at PH bifolds, if such a thing exists. Things might have moved on in the year or two since I last looked at this.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286320#Comment_286320 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286320#Comment_286320 Wed, 13 Jan 2021 16:13:47 +0000 djh Posted By: lineweight(b) Yes, I see that in principle, although you could argue this is an issue even if you bridge the leaves further down somehow.
It all depends on the foundation design. A passive slab with an outer wythe supported on separate strip foundations is probably going to be about the worst case, and a trenchfill foundation with two brick wythes on top is likely about the best case. Avoiding such issues is one advantage of not using cavity construction for me.

My understanding was that stuff like compacfoam is only strong in compression, not designed to span across gaps, but I might be wrong.

Once you've committed to putting it in, you can safely join the construction underneath, I expect. Depends on the exact details I suppose.

perhaps I should look at PH bifolds, if such a thing exists

A quick search for PH bifolds shows that they do exist. The Danish firm Lacuna looks interesting. What they say is that their doors are top-hung. I expect that gets around most of the problem, since the bottom guide rail won't carry much load.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286330#Comment_286330 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286330#Comment_286330 Wed, 13 Jan 2021 17:14:53 +0000 LF

permali glass was used in cryogenic plant design and was really tough stuff.
google says - https://permalideho.co.uk/products/

We used like in these photos
https://www.rilco.com/products/isolation-blocks-additional-components


Sindanyo block was another similar one.

I was only doing heat leak calcs not mechanical and it was nearly 30 years ago.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286350#Comment_286350 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286350#Comment_286350 Thu, 14 Jan 2021 10:07:05 +0000 lineweight
Although this does kind of highlight a disadvantage of cavity construction, yes, it does still sort of exist with other buildups too, because you do inevitably have to bridge the insulation layer with something that's strong enough to walk on.

As I understand it, unfortunately top hung bifolds are usually more expensive partly because you have to provide the suitable structure at high level.

It might just be that if you want to have bifolds and also do things properly, it's not cheap.

(Actually when I said bifolds, I really meant sliders, because sliders tend to have several tracks in parallel and this means you can end up with very deep sills to accommodate)]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286351#Comment_286351 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286351#Comment_286351 Thu, 14 Jan 2021 10:09:40 +0000 lineweight Posted By: LFInsulators - strong - may be of use ?


permali glass was used in cryogenic plant design and was really tough stuff.
google says - https://permalideho.co.uk/products/

We used like in these photos
https://www.rilco.com/products/isolation-blocks-additional-components


Sindanyo block was another similar one.

I was only doing heat leak calcs not mechanical and it was nearly 30 years ago.

Looks interesting but generally I'm looking for something that is specifically intended for the purpose - for confidence and cost reasons.]]> Help please! Condensation in newly converted barn. MVHR vs dehumidifier? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286353#Comment_286353 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16869&Focus=286353#Comment_286353 Thu, 14 Jan 2021 10:40:49 +0000 dickster