Kieran McCarthy: Why are some rooms in my home colder than others?

Builder Advice: What to consider when certain rooms are colder than others
Kieran McCarthy: Why are some rooms in my home colder than others?

we are dealing with either dampness or condensation (given that your are experiencing mould and wallpaper peeling off the wall in question), so we need to isolate the problem and propose solutions.

Hi Kieran

We live in a bungalow built in 1984/86. We have gutted it, replacing doors, windows are triple glazed, the walls are pumped, and attic insulated. The problem is the two end bedrooms are colder than the rest of the house and we now have to remove a fitted wardrobe as my clothes smell mouldy. We have a PIV (positive input ventilation) system in place and there is damp course: also the gable wall of this room is cold and wallpaper won’t stay up on it. There is no sign of dampness on the wall. Our heads are wrecked, can you help solve the problem? Our heating is a stove that works well.

Thanks, Aine Ní Scealligh

Hi Aine,

Thank you for your puzzling query. Clearly if I could see the issue it would be easier to determine what the cause is, but let's run through a few options to at least give you the necessary steps and tools to investigate this issue further.

So, let’s narrow down the problem to begin with. The problem is due to moisture on the wall of the house and mould in the clothes in these bedrooms which you note are cold compared with the bedrooms in the rest of the house. In this case, we are dealing with either dampness or condensation (given that your are experiencing mould and wallpaper peeling off the wall in question), so we need to isolate the problem and propose solutions.

If the damp is purely on the inner surface, I would be leaning more towards a condensation issue
If the damp is purely on the inner surface, I would be leaning more towards a condensation issue

Let’s begin by testing for dampness on this wall. For the wall to be damp for reasons other than condensation, moisture would need to be rising from below, through the wall’s external plaster, or from the eaves on top. You mention that there is a DPC (damp proof membrane) in the wall so I am assuming it isn’t rising damp (which will only rise to about 1.2-1.4m above the floor in any case and appear as a local patch emanating from the floor). Have you checked the condition of the gable externally? Is there any sign of damage to the wall here? If it is from above, it will similarly emanate from the ceiling level and fade out as it gets lower. If it is from the render, I imagine you would see various damp patches on the wall and cracks outside.

The next concern I would have is, is there actually a full cavity in this wall? If not, maybe it wasn’t possible to pump this cavity. I would certainly drill the wall in a few places and ensure there is a cavity evident similar to the other walls of the house. I would also carry out some moisture readings at this time. If the damp is purely on the inner surface, I would be leaning more towards a condensation issue (which would be consistent with the mould on your clothes and the fact that you mentioned these rooms are always cold). If however the dampness was found to be inside your wall (as you drill it) then it would suggest that the wall is experiencing damp penetration likely from the sources mentioned earlier. If you have any concerns here I would advise seeking advice from a damp specialist as they will likely diagnose and indeed fix a damp problem which would be my first port of call.

You have a ventilation unit installed which I am assuming is operating correctly. I would at this stage advise getting this serviced to ensure that the installer is happy that this is the case and that there is no local issue with a vent or such. If I am correct in the setup of this device, however, I am assuming that there are no local vents from this system in these bedrooms unless they have ensuites, so the benefits of this ventilation unit may not be felt in these two end bedrooms.

Kieran McCarthy: 'I would advise getting the ventilation unit serviced.'
Kieran McCarthy: 'I would advise getting the ventilation unit serviced.'

Next, I would look at the location of the bedrooms themselves. Given that they are end bedrooms, are they facing north or indeed east? If so, it is likely that they are not receiving any solar gain like many of the other rooms in the house. (Triple-glazed windows will also reduce the solar gain here). It would be interesting to know if, in fact, you experienced this particular problem before you changed the windows and if the windows have in fact got vents fitted.

And last, but by no means least, I would look at your heating. If I am correct, your heating source is a stove back boiler of some sort. You mention that these two rooms are always cold and damp both in the wardrobes and on the end wall. My fear is that this heating system is losing efficiency as it sends heat to the latter end of your house. It would be interesting to see if the problem improves if you placed an electric heater in each of the bedrooms for a few days to supplement the heat that you feel is missing on these bedrooms.

So, again without seeing the issue and without the benefit of the outcomes of my tests above, my initial thoughts are that the rooms aren’t warm enough, the PIV isn’t adding any particular local value and therefore you may not have enough ventilation. If the electric heaters cure the problem, then you could install wall mounted modern efficient electrical heaters but if you feel some level of the problem still exists (and there is no moisture penetration in the wall) then you could install single room heat recovery units. This involves one core drilled in your wall and an electrical socket power source. A further measure could be to dryline the room but this gets complicated due to the fact that you have insulation already installed in your cavity.

If the problem is due to lack of heat, as I fear it is, and a lack of ventilation, then I believe this will fix it. If it needs further work then you know an insulation assessment is required.

Kieran McCarthy is a building engineer with KMC Homes, serving Cork and Limerick. He is also co-presenter of the RTÉ property show Cheap Irish Homes. Check out Kieran’s new podcast, Built Around You ‘dedicated to helping you build, renovate or upgrade your home’ released every Sunday night at 8pm on Apple podcasts and Spotify and on the ‘Built Around You’ Youtube channel. For more information or to take part in the podcast and share your home build story, follow Kieran on instagram @kierankmc

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