What plywood for roofing

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What plywood for roofing

plywood for roofing

Plywood – one of the most versatile building materials, which is actively used for roofing work and installation of shingles. With its help you can create a solid flooring and avoid squeezing the roof on sloping slopes.

Advantages of using plywood for roofing

Before answering the question, which plywood to use for roofing work, it is necessary to determine the reasons for choosing this material. And here we should highlight the following advantages:

  1. Small weight (the material practically does not create additional load on the rafters);
  2. Resistance to rot, mold and mildew (through impregnation with resins and the use of phenol-formaldehyde glue);
  3. Resistance to negative external influences (the maximum deformation does not exceed 0,02-0,03%);
  4. Moisture resistance (the material is suitable for use in harsh climatic conditions and areas with a lot of precipitation).

Characteristics of plywood for the roof

Choosing which plywood to lay on the roof, you need to pay attention to the following parameters:

  • Brand. For these purposes, the moisture-resistant version, which will not delaminate and swell after rain, will be suitable.
  • Wood. The weight and performance characteristics of the material depend on this.
  • Thickness. This parameter depends on the pitch of the rafters and affects the strength of the flooring.
  • The only parameter that you can close your eyes to is the grade of plywood. Since plywood is used exclusively as a substrate for roofing material, the presence or absence of knots and cracks can not affect the quality of the decking.
plywood for roofing

Birch or softwood plywood for the roof?

The main advantage of coniferous plywood is its lower weight (a quarter lighter than its birch counterpart). At the same time, its performance characteristics remain at a high level.  The material has its own impregnation with resins, and therefore is resistant to:

  • moisture;
  • rot;
  • mold appearance;
  • sharp changes in temperature, etc.

At the same time birch plywood is 25% stronger than material made from softwood veneer, and therefore more often used for roofing work.

Thickness of plywood for the roof

As for dimensions, plywood for the roof should have a thickness of at least 12 mm. Otherwise, the sheets will sag under the weight of the roofing and snow. In this case, the final choice depends on the pitch of the rafters:

  • 12 mm at 600 mm;
  • 18 mm at 900 mm;
  • 21 mm at 1200 mm;
  • 27 mm at 1500 mm.

Do not save on material, using thin plywood and laying it in two layers. Such an approach does not provide tangible benefits. It is better to think in advance about a more frequent arrangement of rafters or the creation of auxiliary crates. Also, experts recommend taking sheets “with reserves” (for example, at a step of 600 mm is not 12 mm, and 15 mm).

The size of plywood for the roof

Choosing plywood for roofing work, it is better to give preference to the maximum possible size of the sheet. This will reduce the number of seams and joints, significantly increasing rates of steam and water insulation.

In this installation technology requires the correct positioning of each sheet – it must overlap several spans and fastened to 3 or more rafters. It is important and the location of the plywood:

  • length – perpendicular to the rafters;
  • the width – on the rafters;
  • vertical seams – in a staggered pattern.

Grade and brand of plywood for the roof

Since plywood is used as flooring and has an additional protective coating of roofing materials with waterproofing, it is acceptable to use grade FC. However, installation takes a long time, and the risk of the roof several times in the rain. And therefore do not exclude situations where the sheet crate swells and delaminates even before installation of shingles.

To avoid this risk, it is better to use plywood grade FSF initially. It is a material with high water resistance, which is achieved through the use of phenol-formaldehyde glue.

As for the grade, any plywood will do for flooring – even with a 4/4 rating. In this case, it does not matter whether the material will be used for subsequent installation of shingles, euro slate or other roofing. And the uncut sheets provide additional security for the movement of roofers on the slope.

So what kind of plywood on the roof is worth choosing? The optimal option is considered material with the following indicators:

  • The thickness of at least 12-15 mm (at a step of rafters 600 mm);
  • The size 2440×1220 mm;
  • made of birch veneer (high strength);
  • Brand FSF (with high water resistance).

Additionally, experts recommend treating the ends of the sheets with acrylic or oil-based paint to improve the vapor and waterproofing qualities of construction.