As Sarah says, you shouldn’t be too worried about small gaps. In the olden days, people used to lay newspaper down on top of the boards before the underlay. You can still do this (it’s cheap, and it’s also a nice thing to look at years later when you eventually change the carpet) - however you can now buy rolls of floor lining paper to do the job! Here’s an example https://www.underlay4u.co.uk/accessories/floor-lining-paper/floor-lining-paper-paper-felt.html. You can also get thermal underlay - we’ve used it in one of our rooms.

I have laid underlay and wool carpets over floorboards in my bedrooms, landing and stairs and they still look good. You could always ask your carpet provider for advice if you need it.

Make sure you have decided what you want to do because your carpet fitters won’t take on extra jobs on the day.

If it were mine I would see if there is a draft coming through….. if there is then I would speak to your carpet supplier and add an extra layer of insulation or upgrade your underlay. If there are no drafts then I would just make sure there are no creaks because you can’t easily fix that after the carpet is laid.

to prevent the draught and even out the floorboard gaps, paperfelt can have some affect but 4mm Harboard or Ply would be even better although there is of course a time/cost implication. It all depends how perfect you need the floor really. Speak to your floor fitter and ask their advice, they may be happy to hardboard/ply the room when fitting the carpet (they will need to use new grippers)

Hi,

Don’t tape over the gaps between the floorboards. In a suspended timber floor, ventilation is essential to prevent moisture build-up and rot in the joists and boards. As mentioned in Carpet Insight, sealing those gaps from above can sometimes do more harm than good if it restricts airflow beneath the floor.

If the void underneath is very cold, insulation is more effective than sealing gaps from above. The best solution is insulating between the joists from below, while keeping air bricks and cross-ventilation clear.

With a wool carpet and 9mm high-density underlay, you should already notice an improvement in warmth and draught reduction.

This is such a good question, and one people often overlook before carpet goes down.

In your case, ventilation wins over fully sealing everything. Those gaps between floorboards actually help the floor breathe, especially with a suspended timber floor and a void underneath. If you tape all the gaps, you risk trapping moisture which can lead to damp or even rot over time.

That said, I completely understand the concern about draughts, especially with a cold void below.

A nice middle ground is:

• Don’t tape over everything
• If there are particularly wide gaps, you can fill those with a flexible filler or use a breathable membrane (like a flooring paper or foil-backed underlay layer) rather than airtight tape
• Your 9mm high density underlay will already do a good job of improving warmth and comfort

If draughts are a big concern, some people use a breathable carpet underlay with a built-in vapour control layer, but again, nothing that completely seals the floor.

So in short, leave most of it as it is, just tidy up any problem areas rather than sealing the whole floor.

You’re definitely thinking about the right things before fitting, which will make a big difference once it’s all down.

- Georgia from Flooring365