Need help with a new garden outbuilding showing damp/mould Damp can be a major issue in the home. Find answers to questions or post your own here.

[ttaylor]

Hi all, first time poster here... I recently employed a builder recommended to me by a neighbour but turns out he's been a nightmare to deal with. I had a brick garden outbuilding built over spring and after completion the skirting boards and the floor at the bottom of the skirting boards is showing signs of damp/mould. I was told it's condensation but I've left the door open for the best part of 5 weeks and cleaned all the mould away with a mould remover spray. The builder said it would go away and wouldn't come back after a month but it was hasn't gone away and with the door closed it grows back again quicker. I also added some dehumidifiers which haven't collected much water. I have uploaded some images and would really appreciate some help/advice on how to fix this. The room gets really hot and I don't think that's right.
The builder was initially uninterested in returning to see the mould and demanded payment (threatened and harassed me). I did not give in and now says he will come take a look at it but since he threatened me I do not feel comfortable with that, can I refuse him entry? The remainder of the balance is due in Nov (which he believes was August) but I want this issue resolved before any payment is given.
Is it a sign of rising damp? Builder says DPC membrane was placed but I don't know how well done it was.

[stoneyboy]

Hi ttaylor
On the face of it you have a nice looking outbuilding.
Presumably it is single skin construction with no insulation on the walls or roof - if this is the case it will get extremely hot in sunny weather.
Presumably there is no natural ventilation so this will make things worse. Also are the patio doors single glazed without solar reflective film?
On payment, you are between a rock and a hard place and I do not envy you. It may be safest to pay up and put it down to a learning experience.
Regards S

[ttaylor]

hey stoneyboy, thank you very much for your reply. On the face of it yeah and overall it's not a horrific build despite some issues, the main one being the mould/damp and lack of ventilation.
I've uploaded some photos of the build - Rockwool was used between the external and internal blocks/bricks and apparently acoustic rockwool for the roof.
So he came a short while ago to adjust the door handle which wasn't locking properly. He said it's normal due to contraction/expansion but this seems very unusual to me, took him about 40mins or so to adjust and resolve that issue. He said he laid a DPM and that when he fitted the joists for the roof the joists were wet and the water would have went down into the insulation but that it was impossible for any moisture to come into the room due to the DPM he said he fitted. When I asked him why he didn't wait until the joists were dry he said he wasn't going to wait. The only ventilation I have is when the door is open or left slightly ajar. I have an air con unit but only use it on occasion when in the room (used as a gym). The doors are double glazed and are fitted with internal magnetic venetian blinds which are constantly down in order to help reflect sunlight. There was a sticker on the glass with Planitherm and http://www.morleyglass.co.uk on it and I assume it has "Planitherm" although it may just be advertising.

Planitherm: Manufactured by Saint-Gobain, it uses a special coating that transforms normal glass into a material that reflects the heat you generate back into your home, rather than allowing it to escape through your windows. The same coating allows free heat from natural daylight to pass through the glass, capturing it to warm your rooms.

Do you think it's worth buying some solar reflective film to put on the glass? Would it make a significant difference?
If so would you fit this on the inside panes or on the external glass?

With regards to ventilation, there still shouldn't be mould growing if there wasn't ventilation? I have looked at something like a Perma-Vent Condensation Control Vent or the Kenwood Humidivent System (apparently pricey) but not sure if this would solve the issue if it's damp?

[stoneyboy]

Hi ttaylor,
It all looks to be a well constructed building and it looks like lack of permanent ventilation may be the problem.
I suggest you fit an extract fan on one side of the building and a vent on the other. The fan needs to run 24/7 it doesn’t need to be more than a 100mm model but pick one designed for permanent running as background ventilation. They are rated around 25w so would cost about 10p a day to run.
I would strongly recommend fitting solar reflective film on the inside of the windows - it’s a relatively cheap fix and can be done yourself.
Regards S