Skylight Installation in Chantry

Chantry roofs sit low. Walk the estate and you can read it off the skyline: long runs of post-war housing built quickly and built shallow, with roof slopes that lie a good deal flatter than the Victorian and Edwardian stock closer to the town centre. That single fact decides more about a rooflight job in Chantry than the brand on the unit, the size of the room or the budget.

It is about 1.4 miles south-west of Ipswich centre as the crow flies, so realistically ten to fifteen minutes across town depending on where the traffic has decided to sit. Close enough that a survey is a short trip and a return visit costs nobody anything.

Why we bring a pitch gauge to Chantry before we bring a brochure

Every pitched roof window carries a minimum pitch rating from the manufacturer. Commonly that is around 15 degrees. Some units are rated down to 10 or 15 degrees only when they are fitted with a specific underfelt collar or sat on a kerb, and the rating is void without it. This is not small print anyone should skip.

Below the rated pitch, the physics turns against you. Water does not clear the flashing fast enough. It sits at the lap, then capillary action draws it back up under the overlap, and it finds the deck. Nothing about the installation is wrong. The unit is simply being asked to work outside the angle it was designed for, and it will leak on a driven-rain day in about the third winter, usually into a newly plastered loft room.

So the first thing worth doing on a Chantry roof is a measurement, not a conversation about glass. We put a gauge on the slope and get a number. Everything after that follows from it.

What happens when the number comes back too low

Two routes, and they are genuinely different jobs at genuinely different prices.

• A low-pitch-rated unit. Several manufacturers make roof windows certified down to 10 degrees with the correct low-pitch flashing kit and collar. Fewer sizes, fewer options, but it is a straightforward pitched roof skylight installation and it keeps the unit sitting in the plane of the tiles. This is what most Chantry roofs get.
• An upstand or kerb. Build a timber kerb off the rafters, lift a flat-roof-type rooflight onto it, and you create your own fall regardless of what the roof is doing underneath. That moves the job across to flat roof rooflight territory, with a different unit, a different weathering detail and more labour. It costs more. It also works on pitches where nothing else will.

We will tell you which one your roof needs after the survey and quote it once. No guessing a figure from a photograph when the whole answer hinges on an angle.

Concrete interlocking tiles and the flashing kit that actually fits them

Most of this estate stock is covered in concrete interlocking tiles, the deep-profile sort with a pronounced roll. That matters because flashing kits are profile-specific. A plain-tile kit fitted to a deep interlocking tile leaves a gap under the side flashing that no amount of sealant closes properly, and sealant is not a weathering detail, it is a delay.

The right kit for a profiled concrete tile has a deeper skirt and a corrugated apron that dresses down into the tile roll. On a VELUX, Keylite or Roto unit the flashing kit is ordered with the window, matched to the covering measured on site.

Loft conversions on ex-council stock: two regulations, one window

Chantry has a lot of loft-conversion potential, partly because the plots are generous and partly because the roof volumes on this stock are usable once you deal with the pitch. On a conversion, the rooflight is doing two regulatory jobs at the same time.

Part B, fire escape. A habitable loft room needs an escape route. Where that is a rooflight, it has to give a clear openable area with a minimum unobstructed opening, sited so the bottom of the opening is within reach of the floor and the sill is not so high that nobody can get to it. That drives both the unit size and its position on the slope.

Part L, thermal performance. The unit has to hit the U-value required for a new opening in a converted space. In practice that means a modern double or triple-glazed unit with a warm-edge spacer and a thermally broken frame, in the region of 1.2 W/m²K rather than the 2.8 you would get from an old unit. See energy efficient skylight installation for the numbers.

How shallow is shallow, and why it changes across the estate

Shallow is not one number in Chantry. The estate went up over roughly two decades and the pitches move with it. Some of the earliest low-eaved terraced blocks sit down around 17 or 18 degrees. Later infill and the private builds that filled the gaps through the 1970s are steeper, often into the mid-20s, which is comfortably inside any roof window’s rating. So the house two doors along can genuinely be a different job from yours, and a figure borrowed from a neighbour is no substitute for a gauge on your own slope.

What the readings tend to mean in practice:

• Above about 20 degrees. Standard roof window territory. Any of the main ranges sits in the plane with a normal flashing kit and the job is quick.
• Roughly 15 to 20 degrees. A low-pitch flashing kit and the manufacturer’s collar, ordered specifically for that angle. Fewer sizes to choose from, no kerb needed.
• Below 15 degrees. A kerb-mounted flat rooflight is usually the honest answer, because a pitched unit is being asked to work outside its design and no flashing detail rescues that.

The condensation trap on a shallow cold roof

A lot of the original Chantry roofs are cold-deck construction: insulation at ceiling level, a cold ventilated void above it, and the covering over that. On a steep roof that void breathes easily. On a shallow one the air path is longer and lazier, and where the eaves ventilation was never generous to begin with, moisture that gets into the void does not clear the way it should.

Drop a rooflight into that situation without thinking about the airflow and you can make it worse, because the opening interrupts the run of the void. We keep the cross-ventilation path continuous around the new opening. Where the unit sits in a converted room the strategy changes entirely: insulation carried up to the rafter line, a vapour control layer sealed to the frame, so warm moist air is not reaching cold timber in the first place. On a shallow roof that detail matters more, not less, because there is less slope helping the void dry out.

What the survey looks at on a low-pitch Chantry roof

The gauge reading is the headline, but it is not the only thing worth measuring before a price is committed. On this stock we also check:

• The covering, and whether it has been changed. A fair share of these roofs were re-covered under a council programme or after a right-to-buy sale, sometimes with a heavier concrete interlocking tile than the roof was built for. That decides the flashing kit and occasionally the battens.
• Eaves and ridge ventilation. Blocked or absent on a shallow roof, and the condensation risk above goes up. Cheap to sort while the scaffold is there.
• The loft volume and the collar height, because a lot of the interest here is loft conversion and the usable height under a shallow ridge is the constraint that decides whether it is worth doing at all.
• Where the water currently goes. Low eaves bring the covering close to the gutter, so the run from a new unit down to the gutter line is short.

Access, at least, is rarely the problem here. The plots are generous by modern standards, there is usually a way round to the back, and scaffold goes up without carrying tube through the house, so the estate does not carry the access premium that a tight terrace does.

Getting a price in Chantry

Every job is surveyed on the roof and priced once in writing. The figure does not move unless you change the specification. A 10-year workmanship guarantee on every installation, installed to current Building Regulations.

We work the same way across the west of Ipswich, in Whitton, Pinewood and out to Sproughton. The full list is on areas we cover.

Request a fixed quote for a rooflight in Chantry. Send the room dimensions and a photograph of the roof from the garden and we will tell you what the pitch is likely to allow before anyone comes out.