Roof construction step by step looks simple on paper: put up the structure, nail on the battens, lay the tiles. On site it turns out that between those three sentences sit a dozen or more decisions, each of which can cost several thousand PLN or several years of peace of mind. The wrong rafter section. A membrane laid the wrong way up. A counter-batten too shallow. Timber at 28% moisture content, closed under the covering in July.

We have run a sawmill in Studzionka near Pszczyna since 1990 and in that time we have supplied the timber for several thousand roofs. This article is the sequence worth having in your head before you order the first cubic metre: stage by stage, with dimensions, standards and the places where things most often go wrong.

Before roof construction starts: the design, the snow and the weight of the covering

A roof does not start with the rafters but with three figures from the structural design: the span, the pitch of the slope and the weight of the covering.

Weight is the most underestimated of the three. Clay tiles together with the supporting battens load the roof structure with 45–85 kg/m², tile-profile steel sheet with battens with 18–21 kg/m². That is a difference of up to four times. Comparing the coverings alone, without the battens, the gap is wider still: 40–70 kg/m² for tiles against 4–7 kg/m² for steel. If you change the specified steel sheet to tiles during construction, a structure calculated for a light covering will not carry the new load — a revised design and heavier sections are needed, for example 8×20 cm instead of 6×16 cm.

The second figure is the snow load to PN-EN 1991-1-3. Poland is divided into five zones. Pszczyna, Studzionka and most of the Silesian conurbation lie in zone 2, where the characteristic snow load on the ground is sk = 0.9 kN/m² — about 92 kg per square metre of ground. Less than that reaches the roof: the load on the slope is calculated with a shape coefficient that depends on the pitch. In the Silesian Beskids, a few dozen kilometres away, zone 4 or 5 already applies, where sk exceeds 2.0 kN/m², more than twice as much. That is why an off-the-shelf catalogue house design has to be adapted to the particular plot, not merely to the taste of the client.

The third matter is the timber. The structural standard is class C24 to PN-EN 338: characteristic bending strength 24 MPa, modulus of elasticity 11 GPa, mean density 420 kg/m³. The class is assigned by strength grading to PN-EN 14081-1, not by a sticker on the pack.

Stage 1: ring beam and wall plate — a roof starts with 14 centimetres of timber

The wall plate is the beam resting on the ring beam, on which all the rafters bear. In single-family houses the usual section is 14×14 or 16×16 cm, with the range found in practice running from 10×10 to 20×20 cm.

Three things that have to be right:

• Damp-proofing. Two layers of underlay felt or PVC film go under the wall plate. Without them the timber draws moisture from the wall and, after a dozen or so years, rots in a place nobody ever looks at.
• Anchoring. L- or U-type anchors set into the ring beam, at the spacing given in the design. Anchors placed “wherever they fit” are the simplest route to a roof that tears off together with the wall plate in a gale, because the uplift load has no way of passing into the ring beam.
• Lapped joints, not butt joints. The wall plate has to work as a continuous beam.

The most common mistake at this stage: leaving out the felt because “nobody sees it anyway”.

Stage 2: erecting the roof structure — sequence, spacing, sections

The structure is assembled in a fixed order: wall plates, then sole plates and posts, then the end, hip and valley rafters, then the remaining rafters, then collar beams or purlins, then trimmers over chimneys, windows and dormers, and finally the dormer wall framing. Reversing that order ends with the geometry of the slopes drifting out of true.

Rafter spacing follows from the weight of the covering:

Rafter section by span (C24 timber, spacing about 80–90 cm):

The values in the table apply to a spacing of 80–90 cm. At 100–120 cm the load on a single rafter rises proportionally and the section has to go up one step, for example from 8×16 to 8×18.

Above roughly 4.5–6 m of span there is no point in making the rafters any deeper — collar beams or purlins are introduced instead. That is already a choice of structural type, which we covered separately in the article on types of roof structures.

Moisture content of the timber. Eurocode 5 (PN-EN 1995-1-1) assigns a roof structure in a closed roof to service class 2, in which the average moisture content of softwood does not exceed 20%. In practice we recommend 18% at most. Freshly felled timber is at 60–80%, after natural seasoning 25–30%, and kiln-dried 15–18%. A beam installed at 28% moisture content will shrink as it dries — joints will loosen, splits will appear along the grain, and curvature will set in that nobody will straighten out afterwards.

Elements are joined today in two ways: with traditional carpentry joints (housings, tenons) or with BMF-type steel connectors and structural screws. Both are correct, provided they follow the design. Fewer fasteners than the documentation calls for is not a saving, it is reduced load-bearing capacity.

Need timber for your roof structure? We cut C24 structural pine and spruce to the dimensions in your design, with delivery across Silesia. We prepare quotations from a roof plan — write to us or see our offer roof structures.

Stage 3: the underlay membrane

The membrane is the layer that carries away water and condensation before they reach the insulation. There are two options:

Minimum weight 120 g/m², the market standard is 140 g/m². It is laid from the eaves towards the ridge, in horizontal courses, the upper sheet always over the lower one. The overlap is at least 10 cm at pitches above 22°, and on shallower roofs 15–20 cm with the laps taped.

A highly vapour-permeable membrane is laid in contact with the thermal insulation, without sag. A slight sag between the rafters applies only to an arrangement in which a gap is left under the film — it then directs any condensation to the eaves instead of letting it stand on the counter-batten.

At the eaves the membrane must finish in the gutter, not above it. Ending it “somewhere above” guarantees staining on the soffit after the first downpour.

Stage 4: counter-battens and battens — this is where ventilation of the slope is decided

The counter-batten does two things at once: it holds the membrane down and creates a ventilation gap above it. Its height is not a free choice for the contractor, it depends on the length of the rafter. For rafters of 5–10 m it is about 3.5 cm, at 15 m it is already 4.5 cm, and at 20 m it is 6 cm. The absolute minimum found in roofing practice is a clear 2 cm.

To that are added the inlet and outlet areas: with rafters up to 10 m the inlet at the eaves should be 200 cm² per linear metre, and the outlet at the ridge 50 cm² per linear metre. A blocked inlet — a tightly closed soffit with no vent, for instance — turns a ventilated roof slope into a condensation chamber.

Battens are chosen to suit the covering: under ceramic and concrete tiles the spacing is usually 31–38 cm; under plain tiles it depends on the laying pattern (single lap 14.5–16.5 cm, double lap 29–33 cm); under modular tile-profile sheet about 35 cm. Bitumen shingles do not go on battens at all — they require full decking of 25–32 mm boards, plywood or OSB. Detailed dimensions, sections and timber species are set out in our article on roof battens.

The overriding rule: the batten spacing is given by the installation instructions of the covering manufacturer, not by a table found on the internet.

Stage 5: covering, eaves and flashings

The covering is laid from the eaves towards the ridge. Before the roofer goes up with the tiles, however, everything that would be hard to fit later is installed: gutter brackets and the eaves flashing, and the flashing kits for roof windows and access hatches. Ventilation cowls, vent tiles and chimney-sweep walkways go on together with the covering, because they are parts of the same system.

The ridge is formed dry — ventilating ridge tape, a batten on brackets, ridge tiles on clips. It is the ridge that provides the air outlet from the slope.

Flashings — the chimney, valleys, abutments to walls, verge boards, eaves flashing — are where most of the leaks reported after the first winter originate. There are no shortcuts here.

One point of workmanship is worth knowing even as a client: sheet metal is not cut with an angle grinder. A burnt coating is a corrosion site that will only show up after a few seasons.

Stage 6: insulating the attic

Insulation goes in last, from inside, once the slope is closed. Typical wool thickness is 25–35 cm, giving a U-value of 0.11–0.16 W/m²K. The 2021 Polish technical requirements call for a roof U-value no higher than 0.15 W/m²K — with typical wool at λ = 0.038–0.040 that means at least 26–30 cm. The layers are laid with staggered joints, with no gaps between boards, and closed on the room side with an airtight vapour barrier. A leaky vapour barrier lets water vapour into the wool and steadily destroys the roof structure from within.

If you leave no gap between the insulation and a low vapour-permeability membrane, everything else stops mattering.

How long roof construction takes, step by step

The best time is spring and summer. Work is carried out at temperatures above roughly 5°C and in settled weather: frost rules out preservative treatment and flashing work, while heat above 30°C makes working with felt, bitumen shingles and adhesive tapes difficult. It is worth ordering the timber in advance — for a simple structure 2–3 weeks is enough, but at the peak of the season lead times at sawmills can run to several months. Once the structure is up, the roof is closed as quickly as possible. A structure that stands in the rain for a month is a structure that goes under the covering wet.

How much roof construction costs — indicative market ranges

The figures below are a review of rates published on Polish trade sites in 2025 and 2026. They are neither an offer nor a price list — the actual cost depends on the geometry of the roof, the region and the availability of crews.

The structure alone is usually 20–30% of the cost of the whole roof. A detailed breakdown of structural costs can be found in the article on how much a roof structure costs.

Frequently asked questions

Where does roof construction begin on site?
With the ring beam and the wall plate, not with the rafters. The wall plate, most often 14×14 or 15×15 cm in section, is laid on two layers of underlay felt or PVC film and anchored to the ring beam with L- or U-type anchors. Only then come the sole plates, the posts, and the end, hip and valley rafters, and finally the remaining rafters. Omitting the damp-proofing under the wall plate is one of the most common and most expensive mistakes there is.

What rafter spacing should be chosen?
The weight of the covering and the span decide. Under tile-profile steel sheet the usual spacing is 90–120 cm, under concrete tiles 70–90 cm, under clay tiles 60–90 cm. The reason is arithmetic: clay tiles with their supporting battens load the structure with 45–85 kg/m², tile-profile sheet with 18–21 kg/m². The final spacing and section are given by the structural design, taking the snow zone into account: zone 2 for Pszczyna and the Katowice conurbation, but already zone 4 or 5 for the Silesian Beskids.

What timber moisture content is acceptable for a roof structure?
The recommended maximum is 18%, with a limit of 20% following from service class 2 to Eurocode 5. Kiln-dried timber reaches 15–18%, while naturally seasoned timber usually stops at 25–30%. Timber that is too wet shrinks after installation: joints loosen, splits appear along the grain, rafters bow. It will not absorb preservative properly either.

Can the membrane lie directly on the wool?
Only a highly vapour-permeable one — with an Sd value of 0.004–0.2 m and permeability of 1300–4000 g/m²/24h. A low vapour-permeability film requires an additional gap between it and the insulation. Whatever the type, a gap formed by the counter-batten has to remain above the membrane: about 3.5 cm for rafters of 5–10 m.

How much does roof construction cost and how long does it take?
General market ranges for 2025 and 2026 are around PLN 350–700/m² for a turnkey roof including material, labour and accessories. The structure alone is usually PLN 110–190/m², that is, 20–30% of the roof budget. On timing: the structure takes from a few days to two weeks, covering a gable roof 3–7 days, a multi-slope roof 1.5–3 weeks, and the whole roof 3–6 weeks. These are general market figures, not an offer — an actual quotation is prepared from the design.

Roof construction forgives very little, and least of all savings on material. It is the one mistake that cannot be put right once the slope is closed. If you have a design and want to know what the timber for your structure really costs, send us your roof plan. We have been cutting C24 structural timber near Pszczyna since 1990.