DIY Doctor UK DIY Forums

Read alot of useful information on this site before posting.
House now rented to my son ( so he may not be helping the problem )

Every winter we have excess condensation to internal walls and mainly the pine end of the building.
The house was built in 1910 with red brick with cavity which i had rendered and dashed some years ago.
Last summer we cleared all the cavity of old mortar probably from when the house was built and rubble was 2 brick
high in most places so a fair bit of crap came out.
I have also added several air brick vents to external walls around the property to help keep the cavity aired.

( question 1 )

Would adding the air brick vents make the cavity colder which in turn would make the internal walls colder which
would not help with the condensation ( dew point ) cold spots which we have just above skirting and corner of walls. ?



Couple years ago i did paint bitumin where i ( thought it was damp ) coming through but after reading on this site,
i have taken off the paint and bitumin and the plaster is dry underneath apart from right at the bottom and corners
of the wall. Also bought son a dehumidifier which is helping dry it out along with some humity sensors so he can see
the readings in other rooms of the house


Another issue we have is water dropplets on the inside of the felt in the attic, the attic was boarded out with foil
backed plasterboard many years ago to use as a storage room as no planning permission and no heating in attic and some
of the boards are getting damp.
I have taken some boards off which reveals the water dropplets on the felt and so i can check the eaves are not blocked to
allow air to circulate around the roof space.

( question 2 )

Could heat rising from the rooms below cause condensaion dropplets on the felt and a possible lack of air although air / draft
seems fine. Would adding extra loft insulation help with this issue although i also intend to check for any cracked tiles
or other roof issues.

thanks in advance

There is no need to ventilate a cavity at all. If condebnstation forms in the cavity it will drop down through the cleared cavity to a point below DPC where it will disperse without danaging anything. Yes the air in the cavity will make the internal wall cooler than it needs to be when the weather is cold.

The condensation in the loft could be both the hot air coming up through the house and the warm air already in the loft. Whatever it is, it needs ventilation which, as our condensation page shows https://www.diydoctor.org.uk/projects/condensation.htm the onlt remedy is ventilation. You must let the warm air out of the loft or it will condense. Usually the condensation is visible as it cannot be absorbed by the surface but when the surface is absorbant, like plasterboard, it will just soak in and go mouldy. Put some vent tiles in or some vent ridge or even an extractor fan

Thankyou for your reply

My son lives in the house now and said it has been colder in the house since we fitted the outside cavity vents so probably not such a good idea.

You are correct about the plasterboard being absorbant and going moldy, especially because it is foil backed so basically the heat is trapped in the attic room, apart from a sky light with a small ventilation latch.

we have a dehumidifier up the attic at the moment and took off some damaged plaster board to allow the room to get ventilation from the roofs eaves.

Would the eaves in the roof be enough ventilation for the attic although i like the idea of the extractor fan has they have helped in the kitchen and bathroom since fitting them.

thanks

Condensation will be caused by too much water vapour in the air. Try to reduce the effects of your daily activity such as cooking or washing which cause condensation.

Using an extractor fan while using the shower, covering pans while cooking and avoiding drying clothes indoors will help. You can also ventilate the house by opening two windows across the building which will create an air flow.

Here are some articles which offer advice on condensation
https://www.permagard.co.uk/advice/stop ... on-windows
https://www.dampproofingbedfordshire.co ... de-to-damp

BrettRendell wrote:Condensation will be caused by too much water vapour in the air. Try to reduce the effects of your daily activity such as cooking or washing which cause condensation.

Using an extractor fan while using the shower, covering pans while cooking and avoiding drying clothes indoors will help. You can also ventilate the house by opening two windows across the building which will create an air flow.

Here are some articles which offer advice on condensation
https://www.permagard.co.uk/advice/stop ... on-windows
https://www.dampproofingbedfordshire.co ... de-to-damp

Thankyou for your answer

As my son is in the house with his girlfriend and baby i cannot guarantee they help. I have installed extractor fans in the bathroom and kitchen and will be fitting trickle vents to all windows next time i'm up there. I know they dont help by cooking without lids and drying clothes on the radiators because their tumble dryer has just packed in, but i did buy them a dehumidifier as it shows the humidity in the room and also got them humidity sensors to see what the readins are in the upstairs of the house. My main concern is that by fitting outside vents to the now cleared cavity is that the interior / exterior walls are now colder than what they should be. I am thinking about covering outside vents with adjustable covers so i can open in summer and close in winter. Bit like a trickle vent lol

Since i last posted, the problem with condensation / dropplets on the inside of felt up in the attic has cured now that i have cleared the eaves and fitted some plastic tubing inbetween the felt overlap to allow more air to circulate. Found a great video here >> https://www.youtube.com/watch?v=QEPzyrynU6Q I am now going to replace and add extra loft floor insulation up in the attic to reduce the heat loss from the rooms below.

My questions are: Should i look at getting cavity wall insulation pumped in or would this cause problems on this type of building.
Also should i insulate between downstairs and bedrooms although there would be radiator pipes and cables to deal with and ways to detect where the biggest heat loss is.

House is comfortable with heating on but with these old red brick house, once heating is off, it quickly goes from being comfortable to being cold again.

many thanks for any replies