New roof installation
In short
Covering a new structure — an extension, a garage, a new build — means designing the whole build-up rather than replacing an existing one: pitch, covering, insulation strategy, ventilation, and how it ties into the roof that is already there.
Also called: Extension roof · New build roof · Roof on a new extension · Roof construction
Signs you need this
- An extension, garage or outbuilding needing its first covering
- A new build or a rebuilt roof structure
- A loft conversion changing the roof shape
- A porch or canopy being added
- An existing roof being extended over new space
A new roof on new structure is a design job before it is a covering job. Everything is open: the pitch, the covering, whether it is a warm or a cold roof, how the ventilation works, and — usually the hardest part — how it joins onto the roof that is already on the house.
Pitch decides the covering, not the other way round. Every covering has a minimum pitch below which driven rain gets past the laps, and it is a hard limit rather than a preference: plain tiles want a steep roof, interlocking tiles will go considerably lower, and below the lowest tile pitch you are into single-ply, GRP, EPDM or lead. An extension designed at a pitch that will not take the tile chosen to match the house is a problem that has to be solved at drawing stage rather than on site.
Matching the existing roof is the aesthetic priority and it is rarely perfect. New tiles against fifty-year-old tiles are conspicuously different in colour for years, so the usual approaches are to source reclaimed matching stock, or — where a large area is involved — to take tiles off a hidden slope of the original roof for the new visible work and put the new tiles where nobody sees them.
The junction where new meets old is the detail that decides whether it leaks. Where an extension roof abuts the existing wall or roof, it needs proper flashings and, on an abutment, soakers interleaved with each course. Where two slopes meet, a valley. Where the new roof runs into the existing one, the coverings have to be woven or the junction lined. None of that is exotic, and all of it is where a general builder's roof tends to fail.
The insulation strategy has to be decided early because it changes the structure. A cold roof has the insulation at ceiling level with a ventilated void above — simple, cheap, needs a proper air path. A warm roof has the insulation above the deck or between and over the rafters, which gives a room-in-roof and no ventilated void, but demands a correct vapour control layer or it condenses inside the build-up. Getting a warm roof wrong produces damp with no visible leak and rots the structure from the inside.
New building work is fully within the Building Regulations rather than the 25% renovation rule, so it needs the full sign-off: structure, insulation to current standards, fire spread where the roof is near a boundary, and weather resistance. That runs through the extension's own Building Control application, which is one of the reasons it is worth having the roofer involved before the drawings are final rather than after.
What the job covers
- Covering chosen against the actual pitch, not the other way round
- Matching to the existing roof planned properly, including reclaim
- Full detailing at abutments, valleys and junctions with the old roof
- Warm or cold roof build-up specified with correct vapour control
- Ventilation designed in from the start
- Coordination with the project's Building Control application
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Will the new roof match the old one?
Closely, rarely exactly. New tiles beside weathered ones are noticeably different for several years. The usual answers are reclaimed matching stock, or taking tiles from a hidden slope of the existing roof to use on the new visible area and putting the new ones out of sight. It is worth deciding which approach before ordering.
Can I have the same tiles as the house on a shallower extension roof?
Only if the pitch is above the minimum for that tile, and often it is not. Every covering has a hard minimum pitch below which driven rain gets past the laps. If the extension is designed shallow, either the design changes or the covering does — and the second option means it will not match. This is a drawing-stage decision.
Warm roof or cold roof?
Cold roof — insulation at ceiling level, ventilated void above — is simpler and cheaper and suits most extensions with a flat ceiling. Warm roof puts the insulation above the structure, which is what you need for a vaulted ceiling or a room in the roof, and it requires a correct vapour control layer. Getting a warm roof wrong causes condensation inside the build-up, which is expensive and invisible.
Does it need Building Control?
Yes — new construction is fully within the Building Regulations rather than the 25% renovation rule. Structure, insulation, fire spread near a boundary and weather resistance all have to be signed off, and it normally runs through the extension's own Building Control application.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.