We have a damp problem in a 1920s semi-detached house we moved into 8 weeks ago. We are not sure if it's a condensation problem, or penetration from the outside, or even rising damp on the ground floor. I have taken pictures of the affected areas:

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The full set can be found here:


The windows are all PVC which looks completely sealed - there don't appear to be any trickle vents. We do notice occasional condensation on the windows in the morning. We need to get the windows replaced with wooden-framed windows again (in accordance with local building preservation-area regulations - originally, this house had wooden-framed windows). Would doing this help? Is there anything we should look out for? Can we get trickle vents on wooden frames?

The walls do not have a cavity. I think there is just two layers of brick, with an external render. The external walls are often quite cold to the touch.

We tried to clean the affected areas with Auro Mould Eliminator a few weeks ago, but it's either been ineffective or it's just the stains that remain. We are going to repaint anyway, but before that, we want to take some preventative measures so that the problem doesn't come back and are looking for advice.

We have been suggested to get the external render of the house looked at in case there are cracks that water is coming in through and get it patched up. Searching around online, people advise getting dehumidifiers to help with condensation. Are there any other measures we can take?

  • Is that a gutter downspout on the wall? If so, I'd start there. What happens to the water from that pipe when it rains? Does it pool around the house? How is the ground sloped away from the area? Try sloping the ground or using extension pipe to discharge the water well away from the house and see if it helps.
    – Mark
    Oct 30, 2016 at 12:35

3 Answers 3


Very interesting situation. First off, replacing perfectly good vinyl windows is not going to help you from what I see on your pics. Simple weeping drains around windows is not going to help much with all the moisture I see on walls, ceilings and floor.

I would suggest you have someone come in with an infrared scanner and make a sweep of the building to determine areas where moisture may be coming from. If the water is coming in from outside through the roof, floor etc., infrared should be able to see it. knowing where the sources of moisture are will help you in making decisions on how to mitigate it.

If this problem is internal condensation, you may need to install some sort of ventilation system. Dehumidifiers certainly would help, but depending on the areas in the house creating the problem may be addressed with better ventilation. Bathrooms, laundry are prime areas for excess moisture.

Since this condition is creating mildew and mold (seen in pics) , I think you should have some professional evaluation before the mold situation becomes a serious health issue.

  • Thanks. I think we will probably get an independent damp surveyor with some tech to test it and advise.
    – Wivlaro
    May 3, 2014 at 17:18

Note: my answer demonstrates an advanced beginner level of knowledge of building science. I know just enough to think I know far more than I most likely really do, so take this answer with a grain of salt and consult a professional as well!

Rand and Shirlock are probably onto something. Let me offer an alternative or perhaps more general hypothesis. Your external walls are made out of porous masonry--brick and stucco (our word for "rendering" here in the 'states). These materials are "reservoir walls" capable of holding a lot of water when they get wet. Since you're in the UK, it's a wet, rainy climate, so the exterior walls can be expected to get wet a lot. Stop the presses!

Such walls have historically worked well because water that enters the wall is able to dry to both the outside and the inside. Outside, sunlight will warm up the wall and dry off the surface, while simultaneously driving water toward the inside in a phenomenon known as "inward solar vapor drive." And heat generated from interior heating appliances dried off the inside of the wall. So where did the water go? It was mostly vaporized and became water vapor.

Now, in old houses, the entire building envelope was really leaky. So excess water in the air could easily leave the house in windy, drafty weather through the myriad cracks and holes in the building envelope. In modern times, we now know that sealing up air leaks improves a building's performance. This may have been done to your house, which I suspect since you mentioned that the historical wood windows have been replaced with modern vinyl ones. However, if we do this to a house with masonry walls and no insulation (you said "The external walls are often quite cold to the touch"), suddenly the humidity in the interior air has nowhere to go. What happens to warm, humid interior air? It condenses into water on the first cold surface it hits. And if your exterior walls are un-insulated and cold to the touch from the interior, that's where the water is going to appear.

What can you do about this? Well, you have a few options:

  1. Insulate the walls. If you add some thermal insulation on the exterior of your walls, not only will they be warmer on the inside (which will make the house more comfortable and also lower your heating bills), but the insulation will go a long way to keep the masonry in the wall from getting wet in the first place. This is probably the best solution, but also the most complicated and expensive. Adding exterior insulation is also very popular and common in Europe, so you will probably find many contractors able to do the job properly.

  2. Keep the walls from getting as wet. Gee, what a surprise. In the UK, wet walls are probably inevitable. But the drier you can keep them, the better. One way would be to add a new exterior siding which includes a "ventilated rainscreen gap." When water strikes the new cladding and inevitably gets driven behind it due to wind and sunlight, instead of draining right into the existing wall, the ventilated gap will cause it to drain down a passageway and exit the bottom of the wall, away from the house.

  3. Get some more interior ventilation. Your damp problem is probably compounded by a lack of adequate air leakage if the building has been retrofitted for increased energy efficiency through air sealing over its lifespan. Air leakage is bad because it robs the house of heat, but it also carries out moisture. There are now mechanical devices called Heat Recovery Ventilators (HRVs) whose job is to provide ventilation while retaining the heat in the air. Such a device, if carefully installed, might be worthwhile.

  4. Remove any existing moisture barriers in the wall. I can't quite tell from the third picture, but that looks like wallpaper. If it's vinyl wallpaper, you need to remove all of it, because it's serving as a moisture barrier. When water in the wall tries to dry toward the inside of a wall with vinyl wallpaper, it gets stuck when it hits the vapor-impermeable vinyl and condenses there, eventually dripping out the bottom.

There are some things you don't want to do that might seem like a good idea:

  1. Don't add any moisture barriers on either side of the wall. If you block off either side of the wall from being able to absorb or release water, you've (theoretically) stopped water from entering, but also exiting! So where's it going to go? Either out the other side of the wall, or it will condense just under the vapor barrier and cause mold, rot, etc.

  2. Don't get a dehumidifier and call it a day. This would be putting an expensive band-aid on a real problem. The machine will be running 24/7 and you'll be constantly needing to empty it. Eventually it will silently break or you'll turn it off for a few days when you're out of the house and the problem will return.


I am by no means knowledgeable in these matters in the least, so take this for what it's worth, but there is something I’ve heard recently and it may pertain to your situation. Modern exterior wall construction has a vapor barrier that is on the living space side of the wall, which prevents the moisture from our bodies, cooking, bathing, houseplants etc. to penetrate and condensate inside the wall when it’s colder outside.

In the 1920’s masonry walls like you describe wouldn’t have a vapor barrier and would instead rely on the wall’s ability to naturally evaporate this moisture through the brick and/or stucco to the atmosphere. In the case of stucco, if you needed to spruce up the outside of your home you’d hire a mason and they’d apply a fresh thin coat of cement, which I think is called whitewashing.

Then came along modern, plasticized, exterior paints, which now puts a vapor barrier on these old masonry walls where none was before, and not on the inside of the wall where it should be, but on the outside. Now the wall can saturate, because it can no longer release the moisture to the atmosphere.

What you probably need to do is hire a company that can coordinate sandblasting off the paint and restore the exterior to a 1920’s era condition, while replacing the windows to the wooden ones. And then maybe someone can come up with a creative process to speed up the drying out on the inside, so that the interior walls can be repaired and restored. After that anyway that you can form an interior vapor barrier would help, several coats of a high quality latex paint, vinyl wallpaper and so on.

  • I do not recommend an interior vapor barrier unless the outer surface of the masonry wall is kept warm and dry (e.g. with insulation). If there's an interior vapor barrier, what's going to happen to rainwater that gets into the wall but can't dry to the outside? It's going to condense on the vapor barrier, that's what.
    – iLikeDirt
    May 4, 2014 at 16:02
  • Yeah, I don’t know! At least in my climate, I’m tempted to say empirical evidence doesn’t support your opinion of no vapor barrier or the inward solar vapor drive theory, but my evidence would, for the most part, only pertain to more contemporary well insulated walls. I do believe that these homes and buildings didn’t start out with mold growing, damp walls and that something since has changed. And that’s the elephant in the room that I think you’re ignoring… what has changed is plastic paint.
    – Rand
    May 4, 2014 at 19:00
  • Dunno what you mean by "plastic paint" but modern latex paint is actually fairly vapor-permeable, even after a few coats. At least in the USA, what often changed to precipitate these kinds of conditions were the installation of vapor barriers in walls that previously dried to both sides, and the installation of air conditioning in previously un-air-conditioned buildings, which created new cold surfaces for water to condense on.
    – iLikeDirt
    May 4, 2014 at 19:10

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