Insulation in Loft, Under the Water Tank and Condensation Issues...

23 Jan 2021
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Maidstone, Kent
United Kingdom
Hello All. I need advice regarding my loft, specifically insulation under and around the cold water tank. There is a bit of a story to explain everything that has been going on with my loft leading up to this and for that I apologise in advance if it is a bit long winded.

Early last year it was discovered that the ridge line on my neighbours property had no felt under the tiles and this progressed onto my property. I noticed that the top of the timber along the ridge was damp and we had roofers install breathable membrane installed along the ridge line.

FYI. The rest of the roof has old bitumen style felt under the tiles and the whole space has approx. 150-200mm of loose fill insulation installed by British Gas around 2005-2010 and is 50% boarded. The house is a staggered terrace and was built around 1970.

A few months ago we then get water coming in through the roof into one of the bedrooms due to a broken tile and damaged felt in that area. This has now also been repaired and the felt above that area was replaced with new breathable membrane. (thank goodness for insurance)

At this time I also made a new loft hatch. The old hatch was a bit of badly fitting MDF with some insulation roll in a plastic bag stuck to the other side. The new hatch is snugly fitting plywood with draft excluders around the edge and 200mm of solid insulation on the loft side.

Now to get to the main point. My house uses a very large cold water tank in the loft on a raised platform made out of floorboards, a good 40-50 cm above the ceiling below. The tank has insulation pads wrapped around it, an MDF lid and another insulation pad on top of this. The pipes have Polyethylene foam pipe lagging around them and I have a small tube heater sitting under the horizontal section of the pipes. Under the tank there was no almost no insulation, maybe 20-30mm at most.

Now, what I have done is removed all the insulation from under the water tank and built a box around the open area under the tank out of 25mm solid insulation blocks and enclosed it so that any warmth coming up from the room below comes through the plasterboard ceiling and is then directed onto the platform under the water tank and cannot escape into the loft space. Is this a good idea, or is it stupid and am I asking for trouble? Will this keep the tank warm and/or could I risk causing condensation inside this box and damaging the ceiling and/or platform?

To make this more interesting I also started to notice condensation in the loft, especially under the eaves. I have been given a few spare felt vents by my neighbour (he was also having condensation issues) which have made a noticeable difference, and I am having a roofer (the same one who fixed the leak and seems to really know his stuff) install some tile vents and also more vents in the eaves to give it the ventilation it needs next month.
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