Installing a Roof, Section by Section

A roof is built in a fixed order for a fixed reason: each stage covers the one before it permanently. Once the covering is on, nobody sees the bracing again for thirty years.

Installing a Roof, Section by Section — practical guidance from the team running roof installation on the Garden Route. Below is the sequence stage by stage, what has to be right at each one, and the specific moments where it is worth going to look before the next stage covers it up.

Stage 1 — Wall plate and setting out

The wall plate is the roof’s foundation. It must be level, straight, continuous and properly anchored into the wall below.

Anchoring is the part that matters most and the part most often skimped. The wall plate resists uplift, and if it is simply bedded on the wall with nothing tying it down, the roof is held on by its own weight. On the Garden Route, where wind uplift is a live load, that is not adequate.

Level matters because every truss sits on it. A wall plate out of level puts every truss out with it, and the error shows up at the ridge line and in the covering courses.

Setting out fixes the truss spacing and the position of the first and last truss, worked from the eaves so the covering courses land correctly.

Go and look: that the wall plate is continuous, level, and visibly anchored down at regular centres.

Fixings and flashings deserve naming because they are where coastal roofs fail first. Sheeting screws are specified by material and coating class for the exposure, not picked off whatever is in the bakkie, and on a coastal site the fastener and the sheeting have to be metallurgically compatible — a plain steel screw through a Zincalume sheet within sight of the sea is a galvanic cell with a predictable end. Flashings and rainwater goods should come in the same coating and colour system as the sheeting, which in the Chromadek and Colorbond ranges they do.

Stage 2 — Trusses and bracing

Trusses arrive as an engineered set designed for this specific roof, its span, pitch, covering weight, wind zone and any point loads.

Inspect on delivery. Nail plates knocked partly out during handling are common and easy to miss. A plate that is not fully seated is not the joint the engineer designed. Damaged trusses are repaired to the manufacturer’s instruction or replaced.

Erect plumb, at the design spacing, on the wall plate, with temporary bracing as work proceeds. A row of unbraced erected trusses is genuinely unstable.

Tie down to the wall plate with straps, hoop iron or proprietary connectors at specified centres. This is the roof’s resistance to being lifted off.

Then permanent bracing to the truss designer’s layout. Diagonal bracing in the plane of the rafters, longitudinal bracing along the length, web bracing where required. This is the most commonly omitted element in South African roofing, and the most commonly cut afterwards by someone getting a tank into the roof space.

Go and look: count the bracing against the drawing, and count the tie-downs. This is the single most valuable inspection you will make, and it takes two minutes.

Stage 3 — Underlay and battens

Underlay first, and it is more important than it looks. On a tiled roof it is the actual waterproofing layer — the tiles shed most of the water and the underlay catches wind-driven rain, water backing up behind a blocked valley, and run-off from any cracked tile.

It must lap correctly down the slope so water runs over each lap rather than into it.

It must discharge into the gutter, not behind it. This is the detail most often got wrong and its consequence is water delivered straight into the fascia and the rafter ends — which is why so many older houses have rot at the eaves.

It must not sag into troughs between rafters, where it will hold water instead of draining.

Battens or purlins then go on at the centres the covering requires, fixed into the truss members rather than wherever is convenient, and set out from the eaves so the last course is not a sliver.

Go and look: at the eaves, that the underlay runs over the fascia line and into the gutter.

Stage 4 — Covering

The covering is the fast, visible part, and there are only a few things that decide whether it performs.

Fixed to the manufacturer’s specification for the exposure — the correct fixing type, at the correct centres, with closer fixing in perimeter and corner zones where wind uplift concentrates. A uniform pattern across a coastal roof is under-fixed exactly where it matters.

On sheeting: screws through the crest, never the pan, with the sealing washer compressed just enough to seal and not so far that it extrudes. Overdriven screws deform the crest and the washer; underdriven ones leak.

Sheets rolled to length wherever the roof allows, so there is no end lap to leak.

Cutting with nibblers or shears rather than an angle grinder, and the roof swept clean at the end of each day. Hot swarf embeds and rusts in place, and it is the most avoidable coastal roofing failure there is.

On tiles: correct headlap and sidelap for the pitch, and mechanical clipping at perimeter, verge and ridge and further in on exposed sites.

Go and look: at the roof surface for swarf or grinding dust, and at a few screws to see whether the washers are sitting properly.

Stage 5 — Flashings, rainwater goods and handover

The covering rarely leaks. The junctions do, and this is the stage that separates roofers.

Ridge and hip — bedded, or a mechanically fixed dry system, which avoids the classic cracked-mortar failure.

Valleys sized for the catchment, lapped in the right direction, with the covering cut back far enough that the channel is not obstructed.

Abutment flashings formed in metal and dressed into a chase or under a cover flashing. Not a mortar fillet, which is a rigid material bridging a moving joint and always cracks.

Penetrations with proper flashing units, including any solar mounting.

Gutters and fascia — sized for the roof area and rainfall, on brackets at adequate centres fixed into sound timber, at a consistent fall, discharging somewhere that takes water away from the building.

Handover: the A19 certificate, truss and bracing drawings, the covering manufacturer’s warranty documentation, our workmanship guarantee, and a short maintenance note. Collect all of it at the time — reconstructing an A19 after the ceilings are up is expensive.

Frequently asked questions

What order is a roof built in?

Wall plate and setting out; trusses erected, tied down and braced; underlay; battens or purlins; covering; then flashings, valleys, ridge and rainwater goods. The order is fixed because each stage permanently covers the one before it — once the covering is on, the bracing and the tie-downs are effectively invisible for the life of the building.

When should I inspect a roof under construction?

Twice, at minimum. Once after the trusses are up and braced but before the underlay goes on, to count the bracing against the drawing and check the tie-downs at the wall plate. And once after the underlay is laid but before the covering, to check it laps correctly and discharges into the gutter rather than behind it. Both are two-minute checks of things that become invisible afterwards.

Why does the underlay have to go into the gutter?

Because the underlay’s job is to collect water that gets past the covering and drain it out at the eaves. If it stops short of the gutter, or turns down behind it, that collected water is delivered straight into the fascia and the rafter ends instead. It is one of the most common installation errors and it is the reason a great many older houses have rot at the eaves with no visible leak anywhere.

What is the most important stage of a roof install?

Bracing and tie-downs, because they are what resist wind and because nobody ever sees them again. A truss is a flat frame with almost no stability out of its own plane; the bracing turns a row of them into a stable structure, and the tie-downs hold the whole assembly onto the building. Both are commonly skimped and both are invisible once the ceiling is on.

Can a roof be installed in wet weather?

Parts of it, cautiously, and it is generally a poor idea. Trusses should not be left standing unbraced in wind, timber that gets soaked moves as it dries, and an underlay laid onto wet timber traps moisture. The bigger point is programme: on the Garden Route, getting a building weathertight before the wet part of the year is the single most valuable scheduling decision, and it is worth reorganising a start date for.

What should I receive when the roof is finished?

The A19 certificate for the erected structure, the truss design and bracing drawings, the covering manufacturer’s warranty documentation, the contractor’s written workmanship guarantee, and a maintenance note. Keep the truss drawings in particular — they are what an engineer will need if you ever want to add a geyser, a tank or a solar array.