Loft issue imporperly installed sarking felt

Question

Had a homebuyers survey and this was urgent
Part of the roof void has been covered with what appears to be a non-breathable sarking felt. This has been improperly installed over the top of the timber battens, allowing and moisture caught by the felt to penetrate the timber causing rot. 

Is this a big issue and what is the potential cost. 3 bed house

Mr · Accepted Answer

I would suggest a re roof using  breathable felt and batterns and just resuse the existing tiles and replace any broken ones

Josh · Answer

This is a massive issue and needs to be rectified, i would recommend you have it Re-roofed and while this is going on the roofer can check all the timbers and see if any need replacing due to rot and water ingress. The cost would be down to the size of the roof and what the roof is covered in either blue slate or tiles? These could all need replacing or could be reused depending on the condition of them. a 3 bed semi detached house would be around £11,000 to £12,000 for all the work materials scaffolding and waste removal included.

Thomas · Answer

If it was mine I'd probably bite the bullet and strip it all off, typical three bed semi in West mids I re roof for 7.5k Inc tiles, scaff, premium grade breathable, fascias soffits and twenty year guarantee.

Marius · Answer

Depends if needs a new roof structure ar only reinforcement an average from 4000 to 7000 labour and materials

Colin · Answer

Not big issue if you cut it out and replace with breathable membrane. Job can be done for few hundred in Labour plus materials

Hakeem · Answer

Yes it is u would likely have to redo that part of the roof because moisture can't escape and water may soak into exterior walls

Michael · Answer

yes this a problem eventually the felt will rot and the water will get in to your loft space and cause more damage

William · Answer

This could become a serious problem as wet timber can quickly rot through, as far as cost, it's the materials needed that would probably be the more expensive, rather than the cost of the labour.

Dan · Answer

This is a potentially serious issue, especially over the long term, but it’s very common in older houses — and fixable.

Here’s a clear breakdown of what this means, why it matters, and what you’re looking at in terms of risk and cost.

🧾 Summary of the Issue
Your homebuyer’s survey is saying:

Non-breathable roofing felt (likely bitumen-based) has been installed on top of the battens, not underneath as it should be.

This incorrect method traps moisture against the roof timbers (battens and rafters).

That moisture can’t escape, leading to timber rot, especially in cooler, poorly ventilated roof voids.

🔧 Why It’s a Problem
Roof structures need ventilation or breathable membranes so timber stays dry.

If moisture from condensation or leaks gets trapped, it can decay the battens and rafters, weakening the structure.

It could eventually cause tiles to loosen or even roof failure in bad cases.

🛠️ Is This a Big Issue?
✔️ If the rot is localised and recent:
You may just need to remove the non-breathable felt in affected sections and replace some battens.

Add proper breathable membrane and/or improve roof ventilation.

❌ If the rot is widespread or advanced:
You could need to strip large sections of the roof, replace battens, and fit a breathable membrane across the whole roof.

That becomes a re-roofing job.

A roofing contractor will need to inspect the extent of damage to confirm.

💷 Estimated Cost (UK, 3-Bed House, 2025)
Scope	Description	Approx. Cost
Minor local repair	Remove faulty felt, replace few battens	£400–£800
Moderate section	Strip & replace felt/battens on one side	£1,200–£2,000
Full re-roof (worst case)	Remove tiles, replace felt/battens, re-tile	£5,000–£10,000

🧱 Full re-roof would include breathable membrane, new battens, reuse or replace tiles, and correct fitting.

🧰 What You Should Do Next
Roofing inspection: Get a qualified roofer or surveyor to assess how much timber is affected.

Request photos of any rot found — especially rafter ends or battens.

Check roof ventilation — this may need improving with soffit or tile vents.

If buying the property, use this to renegotiate or request repairs before completion.

✅ Bottom Line
This can become serious if ignored but is often fixable before major structural damage occurs.

Costs vary greatly, so getting a roofer to assess it properly is key.

It’s reasonable to treat this as urgent, not emergency — unless there's already major rot.

Loft issue imporperly installed sarking felt

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