Roof advice please

[Nicketisa]

We moved into a 42 year old extended bungalow with an EPC rated D. The loft does not leak but the insulation is not great and we want storage space up there. The loft insulation specialist we called wants to remove the old insulation and replace with 300mm new, put air vents in the suffix boards which is fine by us. Now, comes the point where we don't know what to do: the extension (which dates back to 1989) has plastic sheeting between the roof rafters and the laths whereas the original part of the house has bitumen. The guy's advice is to take the tiles off the roof, remove the plastic sheeting and replace with breathable membrane felt as condensation can form on the plastic since it isn't breathable. But as far as we know nor is bitumen. We are talking a lot of money doing this which we had not anticipated. My question is: is this really necessary?

[DrFfybes]

Improving insulation can open a whole can of worms.

Modern roofing felts are breathable, older ones arent. The bituminous ones especially so as over time the overlaps heat and cool and seal together. In one end of the house I went up and pried it apart with a spatula and put sticks in in order to get some airflow into the loft void.

42 years isn't old, but at that age I'm surprised soffit vents weren't installed. I'm also suprised he wants to remove the old insulation, it must be quite poor. The usual practice is simply to cross insulate with more. I put 170mm top up on top of the old 100mm in parts of our the roof, but the 200 year old bit had too shallow rafters to insulate, so we decided to remove the tiles and felt and double them up, which led to finding some deterioration, which led to the house looking like this..


As a friend said when I met him walking his dog this morning "I know you said you had no roof, but I've just been past, and you really do have no roof". The steel is where the old 1 x 8 inch ridge timber was - don't you love modern building regs

The big cost of a re-tile (and at 42 years old the tiles should be reusable) is the scaffolding - easily a couple of £k, actually stripping and re-tiling is 2-3 days labour and the roofing membrane and battens are pretty cheap. The risk is that the extra insulation reduces airflow in the loft and increases condensation, which leads to damp and rot. A decent installer will keep airflow clear.

I would be inclined to get a second opinion, and particularly try a local roofing company for an idea of cost for a refelt before comitting to anything.

Paul

[Dicky99]

We moved into a 42 year old extended bungalow with an EPC rated D. The loft does not leak but the insulation is not great and we want storage space up there. The loft insulation specialist we called wants to remove the old insulation and replace with 300mm new, put air vents in the suffix boards which is fine by us. Now, comes the point where we don't know what to do: the extension (which dates back to 1989) has plastic sheeting between the roof rafters and the laths whereas the original part of the house has bitumen. The guy's advice is to take the tiles off the roof, remove the plastic sheeting and replace with breathable membrane felt as condensation can form on the plastic since it isn't breathable. But as far as we know nor is bitumen. We are talking a lot of money doing this which we had not anticipated. My question is: is this really necessary?

The defacto standard for a modern roof is to have breathable sarking felt which obviates the need for vents to be fitted in the soffit.

If there is a need to strip and refit the roof tiles then that provides an opportunity to install breathable membranes but it would seem excessive to strip and recover the roof purely in order to replace the sarking, assuming that the existing membranes are not in a very tattered state.

Stripping more than 25% of the roof tiles will also necessitate a Buildings Regs application with all the cost and other implications that go along with that. They should know that and if they don't it would set off alarm bells for me.

From what you've described, and without knowing more, it is possible that the company is growing arms and legs on the job. If the membranes don't condense on the underside currently in cold weather, there is no reason to suppose they will in future, particularly if soffit vents are fitted.

If the existing 100mm of insulation still looks plumped up and not flattened or perished, there isn't any need to remove it. It's a dirty messy job to do so and the arisings will likely end up in landfill.

It is more environmentally responsible to overlay new insulation on the old. Before doing so you'd need to construct your desired storage platforms (vertical timber studs bolted to the ceiling joists with a plywood top above the insulation).

I'd say ask them some probing questions about the need for Building Regulations approval, and about why dispense with the old insulation, and be guided by the nature of their responses and if it doesn't smell right get other companies in for comparison.

[Nicketisa]

Thank you for your guidance. I am getting 2 other companies in. The insulation seems ok in places but old and grubby in others. The job to remove tiles, strip plastic lining, remove old insulation, put new one in, board part of the loft and put vents in suffits comes to just shy of 7.5k which is a heck of a lot of money.
Doing the same job without the roof work is just over 4k. The bitumen doesn't appear to be stuck and the plastic sheet on the other side definitely has ventilation through the overlaps.
We do not have any knowledge in this department and fear we could be taken for a ride trying to replace something that was built 36 year ago (extension that is).
I will let the other 2 companies give us their views then question them on these particular points to see what their advice is.

Thank you again.