A conservatory roof replacement looks straightforward on paper. The client wants better thermal performance, the panels are tired, and the quote seems simple enough to write. Then the old roof comes off and the real job reveals itself: a timber frame that’s softer than it looked, a ridge that’s out of true, or a span that doesn’t match the manufacturer’s data sheet. Suddenly a two-day job becomes a two-week one, and the margin disappears with it.
This is the gap between surveying and estimating. An estimate tells you roughly what the job will cost based on what you can see from the ground. A survey tells you what’s actually there — the frame condition, the loading, the junctions, the regulatory status — before you commit to a price or a delivery date.
The checks below aren’t about adding paperwork for its own sake. They’re about protecting your programme, your margin, and your reputation with the client. Build them into your pre-installation process, and the “surprises” stop being surprises at all.
Inspect the Existing Frame, Support and Foundation Clues
Before you touch the roof, look hard at what’s holding it up. The existing frame tells you a great deal about what the new roof can and can’t do.
Record the following on every job:
- Age and construction of the frame — uPVC, timber, or aluminium, and roughly when it was installed.
- Section sizes of the posts and box sections carrying the roof load.
- Condition — check for rot, corrosion, cracked sealant, or water staining at joints.
- Distortion — look for bowing posts, sagging cills, or doors that no longer close cleanly.
- Attachment points — how the frame ties into the house wall, and whether those fixings still look sound.
- Visible settlement — hairline cracks in brickwork, uneven floor slabs, or gaps opening up at the house junction
None of this requires guesswork. If you see cracking that extends beyond surface render, movement at the base that suggests foundation settlement, or a frame that’s visibly out of square by more than a few millimetres over its length, that’s your trigger point to bring in a structural engineer rather than make a judgement call on site. It’s a cheap call to make early and an expensive one to skip.
Measure Geometry and Identify Site-Specific Constraints
Every conservatory roof is a product of its site, and no two are identical. An accurate measured survey — not a quick tape-measure estimate — changes what you can design and order.
Capture:
- Spans and pitch across every section of the roof.
- Hips, ridges and valleys, including their exact angles.
- Roof lights and their positions relative to the structural bars.
- Neighbouring rooflines that might shade the conservatory or restrict access.
- Downpipes and guttering positions, both existing and required.
- Boundary access for scaffolding, material delivery, and waste removal.
- Nearby obstructions — overhanging trees, fences, or utility runs.
A design built on estimated dimensions tends to reveal its errors at the worst possible moment: when the panels arrive and don’t fit. A measured survey lets your supplier cut panels, bars and flashings to the actual building, not an assumed one. That single step removes most of the fit problems that turn a one-day install into a three-day argument.
Check Roof Weight, Loading and Design Assumptions
Solid tiled roof weight isn’t a detail to glance over — it’s a structural input that determines whether the existing frame can safely carry the new system.
Factor in:
- System weight of the specific roof product, which varies significantly between tiled, solid and glazed roof insulation options.
- Wind and snow exposure for the site’s location and elevation.
- Supported spans against the manufacturer’s published limits.
- Manufacturer requirements for bar spacing, fixings and reinforcement.
According to advice by All Seasons Roof, avoid treating “lighter” as automatically “safer.” A lightweight system still needs to match the frame’s design capacity, and an under-specified frame can fail under a lighter roof just as easily as a heavier one if the loading sums were never run for that specific job. Confirm loading figures against the manufacturer’s technical data sheet for the exact product and site conditions, every time. Don’t rely on figures from a similar job down the road.
Plan Drainage, Condensation and Weatherproof Junctions
A roof that looks finished can still fail within its first winter if the junctions weren’t planned properly. Water finds every gap you didn’t account for.
Work through:
- Gutters and fall paths, checking that water has a continuous route away from the structure.
- Flashings at every wall abutment, with no breaks in the weatherproof line.
- Eaves detailing, ensuring ventilation and drainage work together rather than against each other.
- Air and vapour strategy, so condensation doesn’t build up within the roof build-up.
Continuity matters most at transitions — where the new roof meets the house wall, where one roof section meets another, and where flashings overlap. A junction that’s 95% right still lets water in. Walk every transition point before sign-off, not just the main roof plane.
Plan Drainage, Condensation and Weatherproof Junctions
A roof that looks finished can still fail within its first winter if the junctions weren’t planned properly. Water finds every gap you didn’t account for.
Work through:
- Gutters and fall paths, checking that water has a continuous route away from the structure.
- Flashings at every wall abutment, with no breaks in the weatherproof line.
- Eaves detailing, ensuring ventilation and drainage work together rather than against each other.
- Air and vapour strategy, so condensation doesn’t build up within the roof build-up.
Continuity matters most at transitions — where the new roof meets the house wall, where one roof section meets another, and where flashings overlap. A junction that’s 95% right still lets water in. Walk every transition point before sign-off, not just the main roof plane.