Solid Floor insulation and DPM

11 Sep 2014
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United Kingdom
Hi All,

I have an old house 1881 which I bought in May this year, there was a lot of damp to the lower part of the ground floor walls which was hidden by dry lining. I removed all the dry lining and plaster which was sand and cement (really bad to use in an old house) and there was that horrible resin render to the entire outside walls, which I have also removed. There was a screed laid so I broke that up to see if there was a membrane which there was but it was very poorly fitted by way of too thin a gauge and hardly any overlap to the joints and no tape on joints. This was laid on a concrete slab. All walls and floor are drying out now all though a bit slow.

I am planning of laying a new 1200 gauge DPM some insulation (50mm) max due to height restrictions and re-screed but I have read and been told that I should not put down insulation in an old house and even putting down a DPM will cause damp issues because this will force any moisture to be pushed towards the walls and creep up creating damp problems because the moisture has to go somewhere. The walls are all pointed with lime mortar. During all the stripping out I uncovered a lovely brick chimney breast and adjoining alcoves which I want to repoint and leave exposed as a feature but am slightly concerned about potential heat loss through the wall. If I did lay a membrane would any potential moisture get to the walls behind the membrane upstand (approx. 150mm) and evaporate through the lime mortar pointing to the outside. What are you views on my issues?


1) Will a DPM cause damp issues? or will any potential moisture escape through the lime mortar?

2) Will there be any benefit in laying 50mm insulation under the screed? again I have heard conflicting advice before coming on here.

3) Will I notice serious heat loss through the exposed brick wall, I will have a 9kw multi fuel stove in regular use. I have seen many TV programmes where old houses have exposed brick walls. I am planning on dry lining the other two exterior walls to the room,

Long post I know but I would really appreciate some constructive advice.


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