I am thinking about sips construction for the extension and would like to ensure that the thermal qualities in the old part of the house meet the standards in the new.

I want an underfloor heating system throughout (the ground floor) but worry that the old house is too leaky, making it ineffectual as a whole.

I would also like to ask: if you have excellent insulation on the upper floor whether Underfloor heating is sufficient on ground floor only.

We have considered External insulation, but feel the character of the property would be greatly reduced.

The House at the moment suffers from condensation (not v badly, but enough to require painting every few years) and i would really like this to stop.

I do not want to put internal wall insulation in, only to find that the problem is just being covered up and left.

Currently the roof in the old house is well insulated and the house is D Glazed.

Many Thanks

  • Tony Taylor


    Applying high levels of insulation in your extension is a must, try to get that U-value as low as possible, it will pay dividends when energy prices start to rise, as they inevitably will.

    Dealing with the existing property is more problematic, I have worked on a number of heating system designs in stone buildings (mainly churches) and have found that the best method of heating this type of space is with UFH, as it provides a nice even heat throughout.

    The other tip I can give you is to leave a breathable border around the junction between your floors and walls. The Peterchurch project I worked on, had Oak floor with UFH and we left a 100mm border between the edge of the floor and the stone wall, which was filled with Herefordshire pebbles.

    This border allowed the foundations and the walls to breathe and would slowly draw moisture up through the border into the room, where it was evaporated by the heat from the UFH.

    As far as insulation is concerned, the only real options are internal or external insulation, the latter being preferred, as you can usually apply much thicker sections, although as you suggest it will detract from the character of the property.

    Internal insulation is available now with some great U-values and very thin sections, however the prices are still quite high. I think you will need to speak with a building services engineer to work out where the condensation problems are and whether they can be improved with new insulation or some form of ventilation system.

    Let me know if you need any further details.


  • John Ibbotson

    I have a similar question. We are buying a two bedroom brick cottage and plan to add a third bedroom with extended kitchen, cloakroom and utility. The extension will be an oak frame and plan to use SIPs. The existing cottage roof could do with re-tiling so we plan to do this when the extension is being tiled. Assuming the existing roof structure can take the weight, could SIPs be used on an existing roof to improve insulation, or is there a better, lighter or cheaper way to improve the insulation ?
    Many thanks,

  • Ches Chesney

    Ben, I am about to embark on a similar renovation/extension of a stone cottage. I would be very interested to hear what choices you made and the outcome.

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