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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    I'll do that then. Sti gives me a u value of 0.11 which is pretty decent for a victorian terrace I think.

    Any reason to put the ufh 'under the stairs' which will be a cupboard eventually? Or baton it off to separate? I just can't see the best way to get all the floors level.

    You can't exactly tile over 25mm pir can you? Or certainly couldn't self level it after and fit lvt for instance?

    We're still undecided on the final floor finish possibly engineered herringbone timber is a consideration.

    We will be keeping the 1m2 porch tiles as a token 'facade retention' 😂
    • CommentAuthorKenny_M
    • CommentTimeJan 14th 2020
    You may have already considered and mitigated for this, and if so just ignore me, but I have a Victorian/pre-Victorian house where the previous owner covered the original solid hallway floor with modern, less permeable materials, and the result has been rotting at the bottom of skirting boards and door frames.

    It obviously depends on the wall construction and if dpc fitted, but if you fit concrete and PIR to the floor and there is no dpc on the internal walls, then you might have a problem down the line.
    Good point, is this something I can calculate or allow for?
    • CommentAuthorKenny_M
    • CommentTimeJan 15th 2020
    I don't think its something you will be able to calculate for. As I am sure you know, one of the biggest problem with trying to model anything on an old house is that they tend to be quite variable in terms of construction methods and materials. Mine appears to be Victorian because of the bay window, but the bay has actually been built on to an older house. This means that the bay section has a slate damp proof course, and the rest of the house has no dpc.

    If your hallway is solid and the rooms to each side of it are suspended timber floors with good through ventilation then the ventilation should carry away any moisture from those internal walls. If its solid floors to either side then you might have a problem and you will probably need to think about how to deal with this. If the ground where you are is fairly dry then you might not have too much of a problem - maybe breathable paint on the woodwork and walls might be enough to let a small amount of moisture breath out the room.
    Posted By: VictorianecoGood point, is this something I can calculate or allow for?

    I don't know what the definitive answer to this is (I sorely wish I did) but I can offer a couple of anecdotal observations.

    First - it is sufficient to lay down a small (750mm x 600mm) rubber backed mat on our Victorian tiled hall (which is in unusually pristine original condition) to cause a clear issue with moisture accumulation underneath it after just a few short weeks. it would clearly be disastrous to lay down an impervious floor covering across the whole thing. Consequently, we use a traditional carpet runner without backing. (If we had problems with the runner presenting a trip / fall hazard due to slipping I would lay it on top of a length of the open meshed rubber matting sold for for that very purpose but fortunately we don't.)

    The finished level of the hall floor is two steps up from the ground outside which in itself slopes away from the house. The ground as a whole around the whole house is unusually well drained with a deep layer of sand and gravel deposited during the last ice age less than 500mm down.

    Interestingly, the builders obviously anticipated the possibility of moisture issues because the skirting boards in the hall are not timber but some form of masonry (probably lime putty) fashioned to be identical to the boards in the rest of the house. Also interestingly, the door linings and architraves in the hall are timber and go down to floor level but show zero signs of any deterioration even after 120 years.

    I suspect that were we to be imprudent enough as to put an impervious floor covering down it would not be long before we were suffering as Kenny_M reports as the moisture would be forced to try and escape at the edges - just where the door frames and skirting boards are located.
    We had similar, but I think it was condensation on the cold uninsulated surfaces, rather than 'rising' damp. When we insulated the surfaces, the room became warmer and carried more humidity. So condensation became more prominent on the remaining cold bridges, such as the base of the masonry walls. An IR thermometer is helpful to check this.

    My personal theory is that the underfloor of 19thC houses acted as a big cold dehumidifier, that sucked the moisture out of the living spaces, contributing to their longevity.
    • CommentTimeJan 15th 2020
    I expect lead paint also has something to do with the longevity of Victorian woodwork.
    Posted By: djhI expect lead paint also has something to do with the longevity of Victorian woodwork.

    Plenty of post-Victorian woodwork has also been painted with lead based paints - at least five decades worth in fact.

    My judgement, based on many years of observation as well as responsibility for the maintenance of properties of varying ages, is that this is not the main factor in timber longevity.

    For sure, adequate regular maintenance of the paint film is absolutely vital for the longevity of any external timber, but older timber definitely fairs better when abused due to lack of maintenance than the recent stuff.

    it seems to me that some 60s & 70s timber painted whether painted with lead based paint or otherwise has a life that can almost be measured in weeks! (I exaggerate obviously, but I trust that my point is clear.)
    I'm still unsure of best way to carry out the following:

    1. To put UFH 'under the stairs' which will essentially just be storage?

    2. If no to the above, how to isolate the hallway slab from the under stairs slab yet still being able to keep the same floor covering 'continuous'

    3. Whether LVT is a good choice for a hallway with UFH? I see temperatures of 27c being touted around as the maximum which I can't see a flow of even 45c leaving the floor temperature greater than 27c? As the heat will dissipate into the room....

    My mesh arrived today also so I'm good to go, how high should it be lifted off the insulation? I have seen this guide:


    where it appears to just be resting on the insulation. Any reason why it should be lifted any higher perhaps?
    • CommentAuthorGreenPaddy
    • CommentTimeJan 21st 2020
    Hi, could you please just quickly remind us what your floor build up is now going to be. Also, have you dug out the slab under the stairs?
    50mm PIR
    25mm PIR Cross staggered
    16mm pipes in 65-75mm screed with fibres
    Ceramic tiles or possibly LVT
    • CommentAuthorGreenPaddy
    • CommentTimeJan 22nd 2020
    If you have dug out the slab under the stairs, then just continue the above floor build-up, but without pipes.

    If you have not dug out the slab under the stairs, then just add a vertical line of the 25mm PIR at the edge of the stair wall, and under the threshold where I imagine the access door to under the stair storage area will be. You're going to get heat loss into that slab from the air above it, so the small interface of slab to slab won't be such an issue comparatively. Are you more likely now to get some condensation on the under stair slab if you keep it cold?

    Those answers seem too simple, so I'm thinking there must be another level of complexity to your question that I'm not understanding.
    You wouldn't be able to put lvt on top of pir surely for instance? Or even tiles for that matter?

    If the area is pipe free but part of the existing slab then wouldn't it heat up anyway and be prone to cracking as well heat up at different rates perhaps....
    • CommentAuthorGreenPaddy
    • CommentTimeJan 22nd 2020
    I'm definitely missing something here. Please point out my misunderstanding...

    - You are putting 60/70mm screed on top of insulation, which will bring you back to original finished floor level

    - If you have dug out under the stairs (still to be clarified), and you don't wish to have UFH in that part of the floor, then simply do not put UFH in that part of the floor, and just pour the screed over the insulation with no pipes.

    - if you have not dug out the floor under the stairs, it is already at the finished floor level, so if you wish to maintain at the same floor level, you can not add something on top. As it's only a storage cupboard, you could of course lay insulation board ontop of the existing slab (pink foam adhered), and then say 18mm chipboard on top, again pink foam adhered), and put a timber upstand threshold, to form a step at the cupboard door. It must only be 1mx 2m?
    Yep all dug out, I'll just keep the slab continuous and not put pipes in then.

    I can worry about the finished floor thereafter.

    Allow say 15mm for tiles including adhesive?
    Insulation down, is a membrane essential or can I just screed onto the boards?
    • CommentTimeJan 26th 2020
    Posted By: VictorianecoInsulation down, is a membrane essential or can I just screed onto the boards?

    You mean the insulation boards? Are they foil-faced? (sorry, I can't be bothered to read the whole thread :) If so then the problem is that the screed material may attack the foil facing. Obviously it depends on exactly what screed material and exactly what type of foil. But that's one major reason for a membrane on top of the insulation (e.g. a poly dpm). A second is to provide a break so differential movement of the screed and insulation with temperature and humidity don't cause cracks, and a third is to prevent the screed flowing down into cracks between the blocks of insulation. So, it all depends on the details of what you've done.
    Foil backed, traditional screed.

    For the price of it I'll throw one down anyway 👌
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