Advice on damp course/dryrods

takay9

We live in a 1930s house and had a free energy efficient survey yesterday. He detected damp in the walls downstairs and suggested a new damp course being installed, which he said would eventually dry out the walls and slow down heat transfer out of the house.

There aren’t currently any signs of damp anywhere (or when it was replastered 18 months ago) apart from we did get a bit of mould on the skirting boards last year. However - this stopped eventually and I wonder if it was due to a) the plaster not being dried out properly b) using a dehumidifier or c) house getting cold at night. Anyway, it hasn’t happened since though I do find the humidity reading in the house starts to get high from autumn onwards (65-70%) even opening windows. Could this be a sign of dampness in walls or is it usual for a solid brick wall house to have high humidity/condensation?

If we do need to replace the dpc, would
anyone advise we use the dry rods? I thought we could put these in either where the current dpc is or the next brick higher. Any advice/experience greatly appreciated - thank you. 

stuart45

You should already have a DPC in a 30's house, no need for a new one. 

takay9

I should have said - there is a dpc, partially renewed but some of it is slate(?) which may be original/very old 

stuart45

Slate DPC's are fine, even when old. Solid 9 inch walls are.more likely to suffer from penetrating damp than cavity walls, and condensation can also be an issue with uninsulated solid walls. Rising damp is often misdiagnosed with a damp meter.

FreeBear

takay9 said:

We live in a 1930s house and had a free energy efficient survey yesterday. He detected damp in the walls downstairs and suggested a new damp course being installed, which he said would eventually dry out the walls and slow down heat transfer out of the house.

There aren’t currently any signs of damp anywhere (or when it was replastered 18 months ago) apart from we did get a bit of mould on the skirting boards last year. However - this stopped eventually and I wonder if it was due to a) the plaster not being dried out properly b) using a dehumidifier or c) house getting cold at night. Anyway, it hasn’t happened since though I do find the humidity reading in the house starts to get high from autumn onwards (65-70%) even opening windows. Could this be a sign of dampness in walls or is it usual for a solid brick wall house to have high humidity/condensation?

If we do need to replace the dpc, would
anyone advise we use the dry rods? I thought we could put these in either where the current dpc is or the next brick higher. Any advice/experience greatly appreciated - thank you. 

I bet he used a damp meter with pointy prongs on the end - Be aware that those things can only give a reliable reading when used on untreated timber. On any other surface, just way too many contaminants (salts, paints, etc) will render the readings meaningless. See this for more info - https://www.heritage-house.org/damp-and-condensation/the-ping-prong-meter-guilty-of-fraud.html

A 1930s property, I would expect to see cavity walls on the ground floor, but building design was going through some major changes at the time, so solid 9" brick walls are not that uncommon. There would certainly be a damp proof course - Either poured bitumen, lead, slate, or engineering brick. None of these "fail" or need replacing unless the wall is subjected to major catastrophic damage. What usually happens is a build up of surface levels outside which breach the DPC or cause rain splashing up. Gound levels should be ~150mm below the DPC. or when that can't be achieved, 75mm with a gravel filled trench 150-200mm wide. If a DPC is to be replaced effectively, a slot needs to be cut in the wall and a waterproof membrane inserted. Those dry rods do nothing except to relieve you of money.

Currently at 60-70% relative humidity here (temperature around 21.5°C) in this late 1920s semi. During the depths of winter, I'll get a little bit of condensation on the windows, but the walls remain dry - If they were getting damp, the wallpaper would be pealing off and I'd have mould everywhere (which I don't).

Just keep the temperature up above ~16°C, ventilate on a regular basis, and try not to dry huge quantities of washing indoors. Put the money you would have wasted on damp "treatments" to better use by improving the insulation and killing any cold draughts.

daivid

Anything advised after a 'free' consultation should be treated with extreme caution. You say all signs of damp are internal from excess humidity/ lack of ventilation so the steps advised by freebear would deal with that, you could also consider a dehumidifier - particularly for use when/if drying clothes indoors.

I completely agree with the above on 'dry rods' doing nothing, everyone I know who has had them is delighted with them because they have spent thousands and the problem has gone away, the work I've seen has always included digging a shallow trench around the house and filling with gravel. The gravel makes the difference, the rods allow the company to charge thousands rather than a few hundred. Even the gravel is technically unnecessary so long as ground levels are kept correct, though it can look smart and be lower maintenance if done right.

digannio

Does a gravel trench work well even without a perforated pipe at the bottom to take water to the nearest land drain? Or does it always require a pipe inside the gravel bed to prevent pooling?

FreeBear

digannio said:

Does a gravel trench work well even without a perforated pipe at the bottom to take water to the nearest land drain? Or does it always require a pipe inside the gravel bed to prevent pooling?

Depends on how well the soil drains - I'm fortunate to be on sand, so didn't bother with any perforated pipe. On heavy clay, I'd probably look at draining any water away.

Megaross

Odds are that if there are damp issues (the "expert" will be a person looking to sell you something - likely expensive damp remediation that actually doesn't work).

I would quite simply ignore them and wait for an issue with damp to present itself. In older houses you'll tend to find your damp comes from lack of ventilation more often than not as they were constructed to breath - single glazed windows, open chimneys etc.

The problems often come from unsympathetic modernisation, at which point you have lots of options but I would wait until you see issues before you decide how to tackle them.