Does a new roof include new battens and underlay?

No covering is fully watertight on its own. Wind can drive rain up under the laps, and condensation forms on the cold side of a roof. Underlay is the sheet stretched across the rafters, under the battens, which is the back-up for any moisture that slips past the covering, sending it down into the gutter. Battens are the timber strips nailed across the rafters. Each tile or slate hangs from one, so their spacing sets the lap, which is how much each course overlaps the one below.

Together they do the working part of the roof. With perished underlay, one lifted tile lets water straight into the loft. With a softened batten, the nails or clips holding the covering stop biting, and slips follow. A new covering inherits whatever it is fixed to, which is why a re-roof treats these layers as part of one job. For the full run of work, see our step-by-step guide to a Stroud roof replacement.

Once the covering is off, the old underlay is usually torn, brittle or holed where nails have worked through, and patching it achieves little. A repaired sheet also leaves overlaps that were laid for a roof which no longer exists. Battens are a different case, because some survive. We look at each, and one that is sound and the right size for the new covering may stay. The risk with keeping any is the nail holes left behind, because a fresh nail driven into an old hole grips poorly.

There is a fit question too. A new covering often has a different gauge, which is the distance between battens, from the one it replaces. Moving from small plain tiles to larger interlocking ones means setting the battens out again, and natural slate wants its own spacing. Old battens only suit the new covering if the old layout happens to match, which is unusual when the product changes.

Weight enters here as well. A heavier covering asks questions of the rafters, a subject covered in our guide to choosing tile, slate or stone.

Underlay comes in two broad kinds, and the choice decides how the roof void is ventilated. A non-breathable sheet, often labelled HR, stops water vapour passing through, so the loft needs air moving at the eaves. Marley's guidance on cold roofs, which cites BS 5250, asks for a 25 mm opening along the eaves for pitches of 15 degrees or under, and 10 mm where it is steeper. A breathable sheet, labelled LR, laid over a well-sealed ceiling beneath an air-permeable covering, can manage with the ordinary 3 mm of eaves construction, or 5 mm of high-level ventilation.

You do not need to memorise any of that. What matters is that the roofer names the underlay and shows how the loft will breathe, because the wrong pairing can create the condensation it was meant to prevent. Eaves trays, vent tiles and ridge vents belong in the same conversation, and each should be mentioned in the quote if the design calls for it.

Nails and clips cost little, so they are the item most easily dropped from a vague quote. Yet the fixing schedule is what keeps the covering on in a gale. BS 5534 (2014 revision) treats ridge, hip and verge tiles as needing mechanical fixing, since a bed of mortar by itself no longer counts as the fixing, as Marley's guidance on that revision also explains. A tile that can lift in a gust is a tile that eventually ends up in the garden.

Ask what the fixings are made of, and whether every tile is nailed or only some. Ask how the ridge is held too: a mortar bed with clips or screws, or a dry-fix system. MyBuilder's 2026 dry ridge guide gives dry ridge at about £40 to £60 per metre, which shows how one detail can shift a total. Where the quote spells the method out, you can compare like with like. Our note on doing the gutters and fascias with the roof covers the other item that tends to be priced alongside it.

Look for these lines by name, not by implication:

• New underlay, with the type stated.
• New battens, and whether counter-battens, the extra strips that run up the slope beneath them, are used.
• Fixings for the covering, and separately for ridge, hips and verges.
• Eaves and ventilation components.
• A rate or allowance for timber repair once the rafters are visible.

If a line reads only "re-roof" beside a single sum, ask what is inside it. Keeping old battens or underlay is a fair choice only when the quote says so, prices it accordingly and gives the reason. Otherwise the saving comes back later as a second visit from the scaffold.

Once we have surveyed and photographed your roof, the quote covers underlay, battens, fixings and covering, and we give the finished work a 10-year workmanship guarantee in writing. Another item that complicates some quotes is an existing array, covered in what happens to solar panels during a re-roof. The wider picture sits on our roof replacement page.