- Good old slate: why it’s avoided
- The main disadvantages and ways to eliminate them
- Features of the roofing system under slate
- Insulation and protection of the roof
- Slate flooring procedure
Numerous innovative materials entice developers to such an extent that they often abandon their tried and tested slate roofing. Is the slate really so bad or is it worth paying attention to it when installing the roof, as well as the features of its installation, we want to tell you today.
Good old slate: why it’s avoided
Slate is considered a traditional roofing solution. During its existence, slate has acquired both supporters and opponents of its use. It is necessary, however, not only to blindly “poke” into the shortcomings of the material, but also to understand their root cause, to know how to avoid the consequences.
Slate is so disliked by many, primarily due to the rapid loss of appearance. In the first five-year period, the roof grows dull, the appearance of moss growth and general pollution is quite likely, especially in industrial regions, where the air is filled with dust and soot.
Slate is not accepted by ardent fighters for the preservation of the environment because of the numerous myths about its harm to the environment and human health in particular. For knowledgeable people, such “arguments” cause only a condescending smile, because the manufacture of slate from potentially dangerous amphibole fibers has long sunk into oblivion: they were replaced by absolutely neutral fibers of chrysotile origin.
And, finally, the usual logic should have been included: in slate, asbestos fibers are firmly bonded with cement, and natural erosion of high-quality material manifests itself minimally or not at all. Therefore, the only stage at which asbestos can enter the body is the process of cutting sheets during installation. But in this vein, for some reason, there is no mention of the harm to the respiratory system of mineral wool fibers, cement and gypsum dust, which are present in large quantities at any facility under construction. It is enough to take precautions.
The main disadvantages and ways to eliminate them
Claims about the fragility of slate are also greatly exaggerated. Possible destruction of sheets occurs as a result of a violation of the installation technique and improper preparation of the roof substructure. In general, the service life of a well-designed and properly installed slate roof is 30 to 50 years. In practice, even the simplest rules for the operation of slate are routinely ignored, and without this any material will look bad.
Certain corrections must be made taking into account the quality of the material and taking into account its additional processing.
The real disadvantages of slate sheets are easy to list on the fingers of one hand:
- high hygroscopicity, which creates favorable conditions for the spread of moss;
- low ease of installation, because the material is rather heavy and fragile, in inept hands it is subject to massive damage.
It is quite easy to deal with the first fact: there are numerous impregnations and paints for slate that increase the hydrophobicity and durability of the coating, and most importantly, remove the issue of a uniform appearance. Manufacturers offer ready-made solutions in which moisture is no longer afraid of slate from production.
The second minus is more difficult to fight. Although it is quite possible to organize the correct delivery of the material to the object, its lifting and fixing is quite realistic, this imposes additional difficulties in the organization of work and requires the involvement of additional workers. And yet, the economic benefit from slate, even in this situation, will be more than tangible..
If you think about it, the service life of the slate coincides with the frequency of replacement of the insulation. The format of the material provides good ventilation of the under-roof space with a very primitive scheme for making a “roofing pie”. It is also impossible not to mention that the slate coating is subject to fragmentary repair, which cannot be said about any other material of the “economy” class..
Nevertheless, there are objects where slate, with all efforts, cannot be rationally applied. These include, first of all, roofs with complex configurations: with dormers and very steep slopes.
Features of the roofing system under slate
The rafter system for a slate roof is simple, but due to the relatively high weight of the roofing material, it must have sufficient reliability. The rafter pitch is determined in the range from 120 to 200 mm, based on the length of the ramp. The rafters are knocked down, as a rule, from boards 60×150 mm, installing them on the edge and be sure to fasten them with crossbars.
1. Rafter system. 2. Lathing with 60×60 mm bar with a step of 750 mm. 3. Skate support board. 4. Frontal board. 5. Board stop for laying the first row of slate, after laying the slate it is dismantled
The slate does not accept movement in the substructure, therefore, all trusses are reinforced with a common sub-ridge beam, under which supports are mounted with a slope length of more than 10-12 m.
All wood used in the roofing system must undergo natural drying within six months, being in a correctly folded pile. Minor holes that appear as a result of warping are directed into the attic. Careful culling is also necessary: lumber with defects is laid aside and subsequently dissolved for the construction of the sheathing.
The lathing is carried out with an unedged board with a gap of 10-15 cm, if it is planned to cover it with a flat slate. For the wave format, a rare lathing made of 60×60 mm timber is better suited, stuffed with a pitch of 45 to 60 cm, depending on the number of waves and, accordingly, the size of the sheet. After installing the crate, it is recommended to immediately nail down the frontal and wind boards, along the edge of which the direction of the wave is set.
Cross-battening is most important for large slopes where shrinkage and thermal expansion must be compensated for, avoiding overvoltage in the slate. In general, the destruction of the coating most often occurs due to the use of low-quality or poorly dried forest..
Insulation and protection of the roof
It is optimal to cover cold attics with slate. In this case, only the general waterproofing with roofing felt is arranged from the protective layers, which is stuffed with brackets over the crate. If insulation is provided for the roof, the crate is built up with a counter lattice to the desired value, but before that, a windproof membrane is pulled along the beams.
1. Slate. 2. Waterproofing. 3. Insulation. 4. Counter lattice. 5. Rafter system. 6. Lathing with 60×60 mm timber. 7. Skate
An additional single or crossed system of counter-lattice slats is designed to distance the coating to form a ventilation gap. A hydrophobic barrier is mounted on top of the spacer bars. If the external counter-lattice system is crossed, it is allowed to arrange slab under-roof insulation in the upper layer, if required by the thermal engineering calculation.
The main volume of insulation is laid between the rafters and lined with slats, along which interior decoration is possible in the future. Regarding the vapor barrier: depending on the temperature regime in the attic, the insulation in operation can come into contact with both indoor and outdoor air. Cold blowing of insulation is much more common, and for a roof without an attic, it has become an unchanging classic.
Slate flooring procedure
Slate can be laid in two ways. In the first, the roof is covered with full-size sheets. Usually they are prepared on the ground: the edge is trimmed to compensate for the vertical deviation, if necessary, then several rows of holes are pre-drilled into the “comb” according to the pitch of the sheathing beam. Please note that if there is a remote external counter-lattice, it is not recommended to fasten the sheets at the intersection. To determine the position of the support bar, the lacing is pulled along the slope.
The sheet is fed to the roof via two guide tubes. Two workers on the roof pull the sheet with ropes and hooks, one or two helpers from below hook the sheet and support the guides. After feeding the sheet, the ropes are thrown over the ridge, and the lower group passes to the other side to support the slate in a suspended position until the roofers fix it.
It is recommended to fasten full-size sheets with self-tapping screws with a sealing washer, at least two rows of four fixing points. Refusal of nails will slightly increase the cost of the roof, but will give confidence in the reliability and compensating ability of the fasteners. They lead the slate patch, as expected, from the bottom up and strictly along the rows with an overlap of 15-30 cm.
Self-tapping screws with a rubber damping washer or classic slate nails with a wide head are suitable for fastening the slate.
Another method of laying slate involves cutting the sheets crosswise into 3 or 4 strips. The advantage of this method is the easy installation process, in which you can get by with the involvement of only two roofers and refuse the bottom team of workers..
In this case, the overlap between the sheets is less, the 8-wave slate is chosen as the thickest, and each element has only one row of fastening. Roofing using this technology is easier to repair, less susceptible to destruction and in appearance is closer to the tile.
The video presented clearly shows the slate installation process with a lot of useful tips: