Damp meter readings

Barwise

Me and my partner recently bought our home, we opted for a more in depth homebuyers survey to have problems fixed or price of sale negotiated.

We had been in for two weeks, moving in at the start of December when we noticed black mould growing on the master bedroom walls. Over the course of two more weeks it had grown 10x in size and had begun to show dark spots on the wall that resembled damp.

I had a roofer come out who advised us it could be the lead flashing, or the window seals - and that two cracked slates on the roof could be a cause (this was detailed in the survey as a fix for the future, no immediate repair needed, no mention of damp) - following this I had a glassier check the windows, no problems. A friend checked the guttering to find the gutter above the bay window is sagging and heavy downpours will cause it to overflow as it's not a drastic sag. (This wasn't picked up on the survey).

We practice good ventilation, windows open (or on latch) often, good heating, no blocking off air flow - we use a dehumidifier yet it still got to the levels it did in less than a month.

We contacted the surveyor to complain and they had arranged a call out to assess the issue, previously and in the report they had reported normal damp meter readings with no damage. The surveyor did checks while I was present and at the worst part of the wall came back with a reading of 21.7% on plaster (above the bay window). He gave us advice on maintaining the mould and assured us it was just condensation, nothing to worry about, just clean, keep the ventilation going, have your heating on longer, and maybe get some insulation in the lead flashing. They've accepted no liability and told us they can only go off the meter readings at the time of the survey (done late September).

As we're first time buyers, and have no knowledge in the trade, we are looking for some advice. Is 21.7% a normal meter reading as he proposed? Has he given us sound advice, or tried to throw us off the complaint towards the surveyors?

sevenhills

Barwise wrote: »

We had been in for two weeks, moving in at the start of December when we noticed black mould growing on the master bedroom walls.

High up, low down or near the windows? You havnt mentioned the brickwork pointing.

princeofpounds

Photos would help (interior and exterior).

Also any description of the construction of the wall etc.

Do you get any moisture on there or inside the windows early in the morning after a cold night? Even a little? It can be enough.

From doing a little research - the problem is that the damp meter readings don't tell you all that much in isolation. They are normally calibrated to wood. 21% in wood is a tiny bit damp - you generally want below 20%.

Readings from plaster can vary a fair amount due to what's in/behind the plaster (it works on electrical conductivity). Apparently it's often a bit higher, so 20-25% is usually treated as fairly normal. But it's not conclusive in itself and would be easier to understand in context (what were the same readings for comparable plaster in areas that are definitely dry enough?).

We don't really have enough information to speculate effectively, but it does remind me a bit of a wall I had in one of my old houses. It was double-skinned with a cavity, but north facing and overshadowed. A few months after moving in, spotty mould developed. I heated the room, ventilated as normal and there were no problems elsewhere in the house or indeed on any other wall. No apparent problems with the gutter, some minor roof issues that didn't seem to explain it.

Finally I worked out that this wall was under a different, smaller loft space built during an extension. It wasn't apparent because of a false wall in the loft. The space behind wasn't insulated - I figured that out by running my hands along the ceiling at night and realised that the last couple of feet were a much colder temperature. That was enough for condensation to form every night; condensation is partially about relative temperatures as well as absolute.

I don't expect this to necessarily be relevant to you. I'm just pointing out that is is possible to get condensation despite apparently running the house reasonably, and it's not always easy to identify why.

Barwise

High up, low down or near the windows? You havnt mentioned the brickwork pointing.

A combination of all three, worst is top left of the bay window reading at 21.7%, with readings of 16-19 above the bay window along the side, down the sides of the bay windows reading 15, and below the bay windows reading at 13.5-14.5%.

As far as I'm aware the pointing is in good condition and does not need redone or is allowing any water inside.

Barwise

Photos would help (interior and exterior).

As I'm new I cannot provide the photos as MSE will not allow me to post links.

Also any description of the construction of the wall etc.

The outside walls appear to be ov cavity construction predominantly being rendered on the external leaf.

Do you get any moisture on there or inside the windows early in the morning after a cold night? Even a little? It can be enough.

We did originally get moisture on the windows (inside) until we used the dehumidifier daily, at the point of the window condensation the walls look sodden (top left, above the bay window, top right and below the bay window).

The new damp readings were taking after three weeks of cleaning with domestos and water, keeping windows open daytime, and heating on slightly longer during night, plus the dehumidifier. At the time of it being the worst, I can only imagine the % reading would've been significantly higher.

We are going to look into installation of more insulation above the bay window in the lead flashing in hopes this may help to reduce the break outs, but we do fear that it is more than condensation hence the asking of advice, as we would have agreed with the vendor to fix the issue prior to purchase.

RelievedSheff

Welcome to the world of home ownership. Houses have a habit of throwing you a curve ball every now and again.

Does the damp seem to get worse after a period of rain? Or is there no difference from wet days to dry days?

Barwise

Does the damp seem to get worse after a period of rain? Or is there no difference from wet days to dry days?

We had about five days worth of mild rain, then one day of heavy rain which is when we saw the damp rapidly growing.

thearchitect

princeofpounds wrote: »

We don't really have enough information to speculate effectively, but it does remind me a bit of a wall I had in one of my old houses. It was double-skinned with a cavity, but north facing and overshadowed. A few months after moving in, spotty mould developed. I heated the room, ventilated as normal and there were no problems elsewhere in the house or indeed on any other wall. No apparent problems with the gutter, some minor roof issues that didn't seem to explain it.

Finally I worked out that this wall was under a different, smaller loft space built during an extension. It wasn't apparent because of a false wall in the loft. The space behind wasn't insulated - I figured that out by running my hands along the ceiling at night and realised that the last couple of feet were a much colder temperature. That was enough for condensation to form every night; condensation is partially about relative temperatures as well as absolute.

I don't expect this to necessarily be relevant to you. I'm just pointing out that is is possible to get condensation despite apparently running the house reasonably, and it's not always easy to identify why.

Interestingly a trick I picked up from a damp specialist (I know, I know) was to use a remote IR temperature gauge to identify colder sections of a wall as a means of determining the risk of condensation from, for example, missing insulation. He didn't believe the actual temperature, I hasten to add. Now I use the same technique where appropriate.

princeofpounds

Post photos URLs with a gap or dummy characters - someone will repair the link for you in a subsequent post

FreeBear

thearchitect wrote: »

Interestingly a trick I picked up from a damp specialist (I know, I know) was to use a remote IR temperature gauge to identify colder sections of a wall as a means of determining the risk of condensation from, for example, missing insulation.

I know of people that use infrared cameras internally to check for cold spots & poor insulation. It is possible to get cheap attachments that plug in to a mobile phone, or you can even hire one for a day or two.

Bay windows are always a pain in the ar.. especially if they have a flat roof over the top (pitched tiled are not much better). Flat roofs are difficult to insulate, and the covering needs regular attention, as does any flashing.

Barwise

Post photos URLs with a gap or dummy characters - someone will repair the link for you in a subsequent post

Thanks for the tip.

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