This article appeared in the Irish Examiner following a readers question about renovating an old stone outhouse in Ireland.
Q. Hi Kieran
I have an old stone barn/dwelling I’d like to do up piecemeal during retirement on a very low retiree’s budget, and plan to do a lot of the work myself. It’s small but I know I can get two bedrooms into it if I go for an upside down layout. The ground level at the back is very high and I’ll try to reduce but pretty sure I’ll hit rock. I’ve been told I could ‘tank’ the inside? What does this mean and is it a good solution?
Also, what are your thoughts on doing an entire timber frame internally? I know I’d lose some width in the building, as well as the exposed stone character
Many thanks,
Eoin, Castlemartyr
A. Hi Eoin
Many thanks for these excellent questions. Renovating an old building is so rewarding, particularly if it is an old building that belonged to your family or you remember it being in use when you were younger, however, as I am sure you know, it is not for the faint-hearted! Stone as a building product oozes character but it also oozes dampness. When I work with stone I always assume it is wet and work around this, I feel this is the most prudent approach. So, let’s see how you could go about renovating your outhouse and bringing it back to life.
The first thing to consider is whether it was in fact a house or a stone shed as this will have a bearing on any necessary planning permission you may need. A house will typically have a chimney so well worth checking this out now. You may also need a septic tank or treatment unit for this future dwelling and this will certainly require both a percolation test and planning permission so best to have all your ducks in a row now.
When it comes to the height of the ground at the back of the building you are right to have a concern regarding water ingress or damp penetration through the stone walls here. Stone is porous and there were no damp proof membranes used in construction in those days (in fact plastic hadn’t even been invented) so you are relying on the next layer of defence which is using the levels of the building and ground outside to keep damp penetration at bay. In a new building you would typically keep the external ground at least 150mm (6 inches) lower than the new finished floor level and this will do most of the work for you. If you feel the ground local to the house holds water then you would install land drainage (open drain channels around the house) to drain the surrounding area and keep the water table from rising too high near the house, particularly in spells of prolonged heavy rain. This however is far from the current set up outside your building currently.
First of all you have a section of ground that is higher than the house on one side. It is worth reducing it if possible as ‘every little helps’ but if you hit heavy ‘blue’ rock then your hands are tied. A modern rockbreaker will be too powerful and will undoubtedly damage the existing stone walls of your property. If it was the case that you could dig down between the rock and the walls of the property to create a trench whereby you could line the external walls of your house with a stippled (‘egg-crate’ surface) damp membrane against the stone and fill the resulting trench with a single sized say 100mm diameter stone to create a drainage channel then this will certainly take some pressure away from the stone walls.
Inside, we can assume now that the wall is less damp but likely still taking in some dampness, depending on the width and depth of the drainage channel you were able to install externally, if at all. Now let’s see what the options are from here.
You can install another stippled membrane inside. (The stippled nature of the membrane will allow the stone to breathe somewhat). When it comes to the inner lining of the walls I would favour a metal track system over timber. The metal tracks are thinner and quicker to install and there is no likelihood of decay in the presence of moisture or dampness.
Once this metal track system is in place you can fit your insulated plasterboard (dry-lining) to create the thermal envelope. I would also install regular access hatches so you can inspect the cavity regularly to inspect it and maintain it.
I would definitely recommend installing a mechanical ventilation unit in your finished home to ensure good air quality and to censure any dampness or local condensation is kept at bay.
Kieran McCarthy is a building engineer and director of KMC Homes bespoke A-Rated new home builder, serving Cork and Limerick. He is also presenter of a new RTE tv show showcasing deep retrofits in Irish homes due out later this year.
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