Summary
Newly installed roofs can and do have defects. The most common categories are ventilation deficiencies, flashing installation errors, ridge tile fixing failures, incorrect tile gauge, valley construction problems and underlay specification errors. Independent inspection identifies these issues whilst they remain the contractor's responsibility to rectify — before they cause damage that is far more costly to address. See also: Can a New Roof Still Have Defects?
1. Ventilation Deficiencies
Ventilation deficiency is the most frequently found category of defect on post-installation surveys. It encompasses several related but distinct problems:
No Eaves Ventilation Provided
On a cold roof construction — where insulation is at ceiling level and a void exists above — cross-ventilation at eaves level is required under Building Regulations and BS 5250. On many re-roofing projects, particularly where new soffits are installed, ventilation is either omitted or is inadequate for the area of the loft.
Insulation Blocking the Eaves Void
Where loft insulation has been extended to the eaves (as encouraged by energy efficiency guidance), eaves baffles are required to maintain the ventilation path. Failure to install baffles when insulation is extended is a common oversight with significant consequences for moisture accumulation in the loft space.
Non-Breathable Underlay Without Ventilated Counter Batten
Using a high-resistance (non-breathable) underlay on a cold roof without providing a ventilated batten space between the underlay and tile batten restricts the movement of moisture vapour. This is a specification error that can produce condensation damage even when eaves ventilation is present.
For more detail: Do Roofs Always Need Ventilation?
2. Flashing Installation Defects
Flashings are the most critical weather-sealing element of any roof with a chimney, dormer, parapet or penetration. They are also the element most commonly installed to a substandard level.
Step Flashing Not Properly Formed
Step flashings at the sides of chimney stacks should be turned up against the masonry by at least 75mm and cut into the mortar joint (chased in) to a depth of 25mm minimum. Flashings simply tucked behind mortar without being chased in will eventually open and allow water ingress.
Back Gutter Draining Onto the Roof Surface
The back gutter behind a chimney stack should direct water away from the roof surface to the sides of the stack, not allow it to drain directly onto the tile surface behind the stack. Incorrectly formed back gutters cause concentrated water discharge that damages the tile surface and can force water beneath the covering.
Flashing Laps and Clips
Lead flashings that are too large in individual sections are subject to thermal movement fatigue. Code 4 or Code 5 lead should be used for flashings, in sections not exceeding 1.5m, secured with lead clips or tacks. Oversized sections without restraint clips will crack at stress points.
Soakers Missing at Slate or Tile Abutments
Step flashings alone are not sufficient at slate or tile abutments — individual soakers are required beneath the step flashing to prevent water running beneath the flashing at each course. Missing soakers are a common defect on both newly tiled roofs and those that have had flashing work carried out.
3. Ridge and Hip Tile Fixing
This is one of the most consistently identified defects on post-installation surveys. Since BS 5534:2014, mechanically fixed ridge and hip tiles are the standard requirement. Mortar-only bedding without mechanical fixings is no longer acceptable practice for new work.
Many installers continue to use mortar-only bedding, or install mechanical fixings (typically stainless steel screws or clips) incorrectly — too few per tile, in the wrong position, or into inadequate substrate. The consequence is ridge tiles that are vulnerable to wind uplift and that can become a safety hazard as the mortar deteriorates.
This defect is particularly important because it may not be visible — the tiles appear securely bedded, but the fixing is inadequate. Drone photography or direct access is required to confirm whether mechanical fixings are present.
4. Incorrect Tile Gauge
Tile gauge determines the extent to which each tile course overlaps the course below. Minimum lap lengths are specified by manufacturers for each product and are related to pitch — steeper pitches allow less lap; shallower pitches require more. Laying tiles at an incorrect gauge compromises the lap length and reduces the roof's weather resistance.
This defect may not cause immediate problems in dry conditions but can result in driven rain penetration during heavy rainfall at low pitches or in exposed locations. It is difficult to rectify without re-laying the affected tile courses.
5. Valley Construction Defects
Valleys are high-risk areas because they collect and concentrate water from two adjacent roof slopes. Common defects include:
- Valley liners not properly lapped: Insufficient overlap of underlay or GRP valley liner sections, creating potential ingress points
- Valley width too narrow: Valley tiles or liners that are not wide enough for the rainfall load, particularly in exposed locations
- Debris accumulation risk: Valley geometry that allows debris to accumulate and impede drainage
- Swept valleys constructed incorrectly: Tiles not cut to the correct bevel angle, creating gaps at the valley line
6. Gutter Installation Defects
Re-roofing projects frequently include replacement of fascias, soffits and gutters. Common gutter installation defects include:
- Insufficient fall: Gutters require a minimum fall of approximately 1:350 to drain without standing water. Gutters installed level or with negative fall cause persistent standing water, overflow during rainfall and accelerated deterioration of the gutter material.
- Poorly sealed joints: Joints between gutter sections and at outlets should be sealed to prevent dripping onto external walls.
- Downpipe shoes discharging onto surfaces: Downpipe outlets should direct water away from the building into drainage channels or soakaways.
7. Underlay and Membrane Installation
The underlay provides a secondary weathering line beneath the tile covering. Defects include:
- Insufficient horizontal lap between underlay courses — typically a minimum 150mm is required
- Underlay not carried into the gutter at the eaves — leaving the fascia board exposed to water running off the underlay
- Tears or punctures in the underlay not repaired before covering materials are laid
- Felt sag between rafters accumulating water rather than draining to eaves
Expert Commentary
"The defects we encounter most frequently on post-installation surveys are not random — they cluster around specific elements. Flashings, ridge fixings and ventilation account for the majority of significant findings. These are areas that require more skill and attention to detail, and they are also the areas where shortcuts are most likely to be taken. An independent survey targeted at these elements in the weeks after installation provides the best possible protection for the homeowner."
Frequently Asked Questions
How do I know if my new roof has any of these defects?
Many of these defects are not visible to a non-specialist from ground level. The only reliable way to identify them is through a specialist independent inspection. UK Roof Surveys can arrange a post-installation survey within days of instruction.
Can these defects be fixed without replacing the whole roof?
Most defects identified during post-installation surveys are rectifiable without full replacement. Flashing defects, ridge fixing issues, gutter problems and ventilation deficiencies can all typically be addressed as targeted repairs. Early identification is key to keeping remediation costs manageable.
What if my contractor refuses to acknowledge the defects?
An independent survey report with photographic evidence is the basis for formal notification of defects to a contractor. The report documents what was found and when. If the contractor continues to dispute findings, the report is suitable for use in dispute resolution or legal proceedings.
Is there a time limit for claiming against a roofing contractor for defective work?
The limitation period for contract claims in England and Wales is six years from the date of the breach (i.e. the date of the defective installation). Documenting defects with an independent survey as early as possible establishes a clear timeline.
Not sure whether you need a specialist roof survey? Our roof survey checker helps you assess whether further investigation may be worthwhile for your situation.