Cold house and condensation issues

[Precipitate]

My house is large and it takes a lot to heat it. In addition every window is like a square bay window stuck on the outside. This means part of the windowsill overhangs the wall meaning cold air gets underneath and leading to condensation on every window.

We think potential solutions are cavity wall insulation or a positive input ventilation system.

How do you know which to get and who would tell me - cavity wall insulation tradesmen will say cavity wall insulation while positive ventilation system salesman will say that. I don't know what to do and can see me doing nothing and staying cold and damp.

A cavity wall should not be damp. That’s why there’s a cavity. It stops damp from the outside. Are you sure air bricks are clear? That there is no excess water from blocked drains? If the issue is around windows, then this should be fixed. Window cills overhang walls. Ours do. Water should drip off them. So are the windows poorly fitted? Not sure cavity wall insulation is the best idea as it prevents breathing.

I think the op is saying that the walls are damp because of condensation because they are so cold? Cavity wall insulation should sort this out. If it doesn't then you can add the passive ventilation. Insulation will definitely reduce your bills and make the house warmer. Have you checked your loft insulation is up to current recommendations too?

I think there might be a bit of a misunderstanding. Condensation isn't caused by cold air.
its caused by warm air hitting a cold surface.

Solutions are making cold surfaces warmer ie insulation and increasing ventilation which can be contradictory.

Insulating the cold surfaces by whatever means is the place to start

FWIW, we did cavity wall insulation in our 1970s house in May. It made a huge difference to the temperature in winter - the house stays much warmer once the heating goes off. And in summer it definitely helped stop the house heating up so much. For what it coat us, it has been well worth the investment

Are the walls wet/ retaining moisture? That will sink heat out the house. Is your boiler running properly? How old is the house? Terrace? Detached? Roof watertight and gutters clear? Do you need new windows? Are there any leaky pipes? Is the loft too airtight?

So we've just had a new boiler fitted, guttering is fine. House is detached.

None of the walls are damp it's just cold. I have tado thermostats on every radiator which tell me humidity is high. But I can't afford to heat rooms to reduce the humidity all the time. The whole point in getting the tado thermostats was so we can put the heating on in rooms that are being used.

The point about the windows is that they stick out from the house. This means warm air is hitting a lot of surfaces so we get a lot of condensation on the windows. I've attached a picture from Google to illustrate.

I'm not sure if the roof space does have sufficient air flow. How would I check this?

Warm air carries more moisture, heating air increases the humidity.

it can become more noticeable in a room that isnt always heated because theres no residual heat in the walls which increases the cold surface part of the equation.

You obviously dont want to lower the heating so all you can do is insulate to keep the walls warmer and reduce the amount you need to heat air to keep warm.

Opening a window a crack or open trickle vents (if you have them) will help by increasing ventilation without substantially losing heat.

Other things to consider are sources of moisture, not air drying laundry indoors etc.

We have a large sandstone house so no cavity wall and it's really hard to heat. The only solution for us is leave the heating on 19oC 24/7 and run a dehumidifier at 50% 24/7. I have to say the dehumidifiers been really good at clearing the windows, no more mould around the window frames and the house is warmer too.
FYI it's a 6 bed over three storys and our fuel bill is around £600-£700 a month. I hope you find a solution.

How old is your house and how do you know you do/don’t have CWI already?

If you have those ‘stick on’ box bay windows, then there is only so much you can do, and depends on the construction. I presume they are uPVC sealed unit ones? If so all you have left is under the cill and the small roof of the window to check and insulate. I don’t see that cavity wall insulation would help with the bay window issue, though it would help in general.

@amyboo

FWIW, we did cavity wall insulation in our 1970s house in May. It made a huge difference to the temperature in winter - the house stays much warmer once the heating goes off. And in summer it definitely helped stop the house heating up so much. For what it coat us, it has been well worth the investment
THIS
We did this also in our last house.
Game changer.
The neighbour also followed suit.

Cavity wall insulation is your first port of call. Any house that has a cavity should have it insulated; it's ridiculous not to.

You may find it fixes all problems because you will be able to afford to heat your house adequately next winter and condensation won't occur.

For the windows I'd get insulating blinds and thick curtains.

We have a PIV unit. You can buy them on Amazon and ask an electrician to fit it. This works out lots cheaper than a company selling them. I got one installed during my renovation as it solved my mums condensation problem instantly. It pushes the dampness out of the house and makes it easier to heat too.

Yep totally agree. I've been tracking our gas usage this year compared to last. And I reckon we've used around 30% less.... the insulation for our largish detached house cost €3800 (so about £3000).

Right I'll get on with quotes for cavity wall insulation as it sounds like it might make a big difference. Thanks all.