Nicketisa wrote: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.