How to Check Roofing Work: What Every Homeowner Should Inspect

Roofing defects account for 15% of all building defects recorded by LABC Warranty - second only to external walls. And unlike a dodgy mortar joint you might spot from the kitchen window, roof problems often go unnoticed until the ceiling stain appears or the loft starts smelling of damp. By then, the roofer's long gone and the scaffolding's been taken down.

The good news: you can check a surprising amount from ground level, and the critical stuff - membrane, battens, insulation, ventilation - is all visible before the tiles go on. If you're still at the quoting stage, our guide to roofer quote red flags helps you spot problems before work begins. This guide tells you what to look for and when to look for it.

TL;DR Checklist

• Tile courses are straight and even, with proper clipping/nailing per BS 5534
• Lead flashings are Code 4 or 5, with 150mm minimum upstand at abutments
• Breathable membrane is continuous and properly lapped, battens are treated softwood
• Insulation is in the right position - ceiling level (cold roof) or rafter level (warm roof)
• Continuous 10mm ventilation gap at eaves for cold roofs
• Guttering falls at 1:350 minimum toward downpipes, brackets at 1m centres max
• Ridge uses a dry ridge system (or mortar-bedded with all tiles clipped)
• Verge edges have dry verge clips or mortar pointing

The Full Guide

Tile and slate alignment

Start from the ground. Stand back from the building and look at the roof face-on. The tile courses should be straight - each horizontal row running parallel to the eaves and the ridge. Crooked courses are immediately visible and indicate either poor battening or careless laying. Neither is acceptable.

From a closer angle, check that tiles sit flat without rocking. Lifted or proud tiles catch the wind, and in a storm they'll be the first to go. On a pitched roof, tiles should overlap correctly - each tile covering the joint between the two tiles below it, preventing rain from tracking through.

Fixing is governed by BS 5534. The standard changed significantly in 2015, and the requirement now is that every tile must be mechanically fixed - either nailed or clipped - depending on the site's wind exposure zone. In exposed areas (coastal, high ground, tall buildings), every tile may need both nailing and clipping. Your roofer should have done a fixing specification calculation for your site.

Lead flashings

Flashings are the waterproof junctions between the roof covering and walls, chimneys, and other upstands. Lead is the traditional material and still the best option for most applications. Two things matter: the code (thickness) of the lead and the detail of the installation.

Code 4 lead (1.8mm thick) is the minimum for standard flashings. Code 5 (2.24mm thick) is used for valleys, wider flashings, and exposed locations where the lead needs to resist more thermal movement. If your roofer is using Code 3, ask why - it's too thin for most external applications.

At abutments (where a roof meets a wall), the lead should turn up the wall at least 150mm. It needs to be dressed into a chase - a slot cut in the mortar joint - and pointed (sealed) with a suitable sealant. The lead should be dressed tightly against the tile surface below, with no gaps for wind-driven rain to penetrate.

Step flashings (used where a roof slopes alongside a wall) need each step to overlap the one below by at least 65mm. The overall appearance should be neat and regular, with each step following the tile courses. Messy step flashings are a common sign of an inexperienced roofer and a frequent source of leaks.

Felt, membrane, and battens

Before the tiles go on, the roof structure gets a secondary waterproof layer - traditionally roofing felt, now almost always a breathable membrane. This is your backup defence if any water gets past the tiles.

Breathable membranes (like Tyvek or similar) are now standard because they allow moisture vapour to escape from inside the roof space while blocking rain and wind. Traditional bitumen felt traps moisture inside, which is why cold roofs with old felt often have condensation problems.

The membrane should be laid horizontally across the rafters, lapping each course by at least 100mm. It should drape slightly between the rafters (a gentle sag, not taut) to channel any water that penetrates the tiles down to the gutter. At the eaves, the membrane should discharge into the gutter, not stop short of it.

Battens should be treated softwood - untreated battens will rot within a few years. The batten spacing (gauge) depends on the tile type and is specified by the tile manufacturer. It's worth checking this: wrong batten gauge means the tiles don't overlap correctly, and water tracking is the inevitable result.

Insulation position

This is where a lot of homeowners get confused, and where a lot of problems start. There are two types of insulated roof:

Cold roof: insulation sits at ceiling level, on top of the plasterboard between and over the joists. The loft space above is cold and ventilated. This is the traditional approach for lofts that aren't being used as living space.

Warm roof: insulation sits at rafter level, between and/or below the rafters. The loft space is warm. This is the approach for loft conversions and rooms in the roof.

The critical rule: don't mix them. If you insulate at ceiling level but also stuff insulation between the rafters with no ventilation gap, you'll trap moisture in the roof structure. The timbers will stay damp, condensation will form on cold surfaces, and rot will follow.

Ventilation

Cold roofs need ventilation to carry away moisture that rises from the rooms below. The requirement is a continuous 10mm gap at the eaves (both sides of the roof) for pitches over 15 degrees. For roofs pitched at 35 degrees or more, eaves ventilation alone is often sufficient. For shallower pitches, you also need ventilation at the ridge - typically a 5mm continuous gap.

This ventilation path must be unobstructed. Check that insulation at ceiling level doesn't block the eaves gap - insulation baffles or rafter trays should hold the insulation back and maintain the airflow channel.

Warm roofs using breathable membrane generally don't need the same ventilation provisions, but the membrane must be correctly specified and installed. If a non-breathable membrane is used on a warm roof, a ventilated air gap between the membrane and the insulation is essential. Getting this wrong causes condensation, which is the single most common defect in loft conversions.

Guttering

Gutters are simple in principle but frequently installed badly. The gutter should fall toward the nearest downpipe at a minimum gradient of 1:350 - that's roughly 3mm per metre. Too little fall and water pools in the gutter. Too much and it overflows at the high end during heavy rain.

Brackets should be fixed at a maximum of 1 metre apart for standard half-round or ogee profiles. Additional brackets are needed either side of joints, at angles, and at running outlets. The gutter itself should be positioned so that the front edge sits below the line of the roof slope - imagine extending the roof surface downward; the water should hit the gutter, not overshoot it.

Check that downpipes connect properly into the below-ground drainage. A downpipe that empties onto the ground next to the foundation is a recipe for damp.

Ridge and verge

The ridge (the top of the roof where two slopes meet) was traditionally bedded in mortar. Modern practice is to use a dry ridge system - mechanical fixings with flexible rubber or foam seals. Dry ridge is now recommended by BS 8612 and most tile manufacturers because it doesn't crack, doesn't need re-pointing every 15 years, and provides controlled ventilation at the ridge.

If mortar bedding is used, all ridge tiles should also be mechanically fixed (clipped or screwed) - mortar alone is no longer considered sufficient.

At the verge (the edge of the roof at a gable end), dry verge clips are the modern standard. They give a clean finish, resist wind uplift, and don't deteriorate like mortar pointing. If mortar is used, it should be neatly applied and the edge tiles should be clipped.

Common Problems

Condensation in the loft. This is overwhelmingly the most common roof defect. Causes include blocked eaves ventilation, missing or incorrectly installed vapour barriers, mixing cold and warm roof details, or using non-breathable membrane where breathable was specified. The first sign is usually black mould on the underside of the roof timbers or damp insulation.

Lifted or missing tiles after storms. If tiles are lifting in moderate wind, the fixing specification is wrong. Post-2015, every tile should be mechanically fixed. If your roofer says "we only nail every third course" on a new roof, they're working to an outdated standard.

Leaking flashings. Lead flashings fail either because the lead code is too thin, the upstand is too short, or the pointing has cracked and fallen out. Re-pointing is a simple fix. Replacing undersized flashings means lifting tiles and re-dressing lead - much more disruptive and expensive.

Gutter overflow. Usually caused by insufficient fall, blocked downpipes, or gutters that are positioned too far back from the roof edge. During a heavy downpour, watch where the water goes. It should all make it into the gutter and down the downpipes, not cascading over the front edge.

Questions to Ask Your Builder

• "What fixing specification have you calculated for this roof?" - This should reference BS 5534 and be specific to your site's wind exposure zone. If they don't know what you're asking, that's a concern.
• "Are you using breathable membrane, and what product is it?" - The product should be from a reputable manufacturer. Your roofer should be able to name it and confirm it's suitable for the roof type (cold or warm).
• "What code lead are you using for the flashings?" - Code 4 minimum for standard flashings, Code 5 for valleys and wider applications. Anything less is inadequate.
• "Can I see the ventilation gap at the eaves before the fascia goes on?" - This is your chance to verify the 10mm continuous gap. Once the fascia board is fixed, you can't easily check it.
• "Will you be using a dry ridge system or mortar bedding?" - Dry ridge is now the industry standard. If mortar is proposed, ask why and confirm mechanical fixings will also be used.