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Internal Insulation using Marmox

SuperHomes Revamp Forums General Discussion Internal Insulation using Marmox

This topic contains 2 replies, has 2 voices, and was last updated by  Dave Higgins 6 years, 11 months ago.

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    Dave Higgins

    I live in a 1927 semi with 9in solid brick walls with pebble dash rendering. It is 200 metres up a hill in Sheffield so it’s quite windy at times. We have more or less full double glazing and I’ve put 300mm of loft insulation in and draught proofed as far as I can, replaced the old open gas fires with sealed ones and replaced the old aluminium patio doors with properly sealed ones with K glass.

    I’ve thought about external insulation but we have a very high gable end wall and it would cost far too much to do it and I don’t like what I’ve heard about the Green Deal and all it’s complexities.

    I’d therefore like to put in internal insulation myself a room at a time starting with the small bedroom which has 2 external walls and needs decorating anyway. I’m inclined to use Marmox 50mm panels but can’t find any comments from people who have used it. It doesn’t meet the requirement for a U value of 0.3 – it appears to be 0.5 according to this document but I’ve seen it expressed that maybe it would reduce the chance of interstitial condensation to go for 0.5 (and some people seem to believe that the walls might have a U value of 1 rather than the standard 2).

    I think I’d follow the Marmox recommendation of screwing the panels over the old plaster (which is the Sheffield special black plaster which used slag from the steel works and horse hair). I would insulate the window reveals carefully and spend a lot of time sealing it all using the Marmox sealant. If I can I’ll insulate below the floor boards (might not be possible on one wall due to the joist being too close to the brickwork). The internal walls of the room are lath and plaster so I suspect the condensation due to conduction along the side walls may not be too much of a problem. I’d then get a plasterer to skim the whole room and put all the woodwork back.

    Can anyone see any problems with this – or should I go for the more conventional Kingspan / Celotex solution and batten it on the warm side.

    Cheers Dave



    All down to how much time or money you are prepared to expend.
    And how much space you are prepared to lose from the room.
    There’s no such thing as too much insulation these days, what seems to be a ridiculous amount at one time seems normal later.
    Re internal insulation, staircases can be a problem due to the width taken off of them if your stairs are against an outside wall. Also you have to consider what to do in the thickness of floors (ie between floor and ceiling).

    There is also the thermal bridging issues caused by partition walls butting against exterior walls, having to move radiators, pipework. shelving and electrical sockets etc.
    You have to consider the whole house, not just one room in isolation.
    Also you want to be doing the warmest, most lived in parts of the house as a priority
    The main advantage of internal insulation is that it can be done piecemeal as you can afford it.
    There are snags with internal insulation, I went for outside insulation personally. It was a DIY project.

    The main snag with external insulation is the roof may have insufficient overhang/have to be extended. I dunno anything about it’s longevity these days. Some add-on stuff was pretty dodgy years ago, but things have improved nowadays I hear.

    My house here.


    Dave Higgins

    Harold thanks for the reply. I would love to have external insulation but our gable end is too high to do myself, quite apart from all the work removing the pebble dash, extending the roof, replacing the cast iron downpipes and sorting out the block paved drive afterwards – even if I had the money which I don’t.

    I accept that it would be best to do the most lived in spaces but I’d like to do a room which needs work as a trial run, it would remove the time pressures and prove the theory. The other area that needs doing most is the hall and you’re right about the problem of stairs against the outside wall – but 50mm Marmox may fit OK if I remove the plaster and would at least significantly improve the situation we have now.


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