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Groundwork & Foundations

Our old house has widespread damp due mainly to poor sub-floor ventilation. is it worth having a sub-floor fan installed and is it expensive?

I know we need more vents but the problem is that there is a solid-floored outrigger which reduces the exterior wall area available for venting, hence the question about the fan! Is it worth getting one installed, is it expensive and is it likely to cure the problem?

2 Answers from MyBuilder Groundworkers

Best Answer

I think the answer is in your question "Poor sub floor ventilation"! Sounds like you have no underfloor vents maybe? If this is the case and the floors are suspended timber,i would increase the air flow by adding new vents by inserting either a 225mm x 150mm or 225mm x 75mm depending on what room you have to fit...

Also are you sure the damp is not rising damp?
And if as you say it is very damp! be carefull that you dont have wet rot or fugal attack on the flooring timbers.

Good Luck.

Oh i see it was`nt stated that flooring is solid construction.
Without looking its tricky but ventilation is the key, a form of warm air exchange unit or above ground vent will help and disperse the moist damp air and aid in drying. The question is whether you have any rising damp! Are you finding salts coming through the plaster? Or mould on the surfaces?

I would put a post on My Builder for the right specialist to survey the problem and offer you a solution on site,it is far more sensible to look at the area`s and quote on site.
Im sure you can find two or three local to yourself who will offer a free survey and quote!
I am based in Essex and offer free Surveys/Quotes.

As for costs these varey from a basic plastic vent with a internal closer,then onto a expelair or heat recovery unit.
Depending on your property needs it could be under a £100 and if needed 2 or 3 heat recovery units it will be another 0 on the end of the previous price.
A visit would be needed to put your mind at ease as these quotes are hyperthetical.

Hope you find a solution to your problem.


Answered 12th Jul 2011

Hi I am working on a few houses in Ealing at the moment and the properties were built over a hundred years ago. They all have three 9" X 6" airbricks in the front (two eitherside of the bay and one under the front step). In two of the properties they have only two in the rear as on one side they have a solid floor for the kitchen. In these two properties the soil and bricks below dpc are slightly damp, but above the timber and brickwork is dry.
In the third property the installation of a solid floor across the whole of the rear has meant introducing vent pipes cast in the slabs.
In all three properties the fact that they have so little ventilation means that the system of natural ventilation is adequate to reduce moisture.
So if you have `widespread damp` then it is likely to be rising due to the breakdown of the damp proof membrane.
Somebody needs to have a good look with areas of floor boards removed.
Good Luck. Rob K


Answered 23rd Nov 2011

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