Larch Roofing Shingles
Characteristics
Our Larch shingle is sourced exclusively from locally grown timber. Intended for exterior use the heartwood conforms to the tolerance of 10% sapwood specified in the Annexes to DTU 31.2. Whilst you may find some traces of sapwood in individual pieces we make every effort to ensure this is strictly minimal.
THICKNESS: 16 mm
WIDTH: 107 mm / 134 mm / 160 mm
LENGTHS: 1.70m or 2.50 m to be cut to size by you, Ask us for details.
WEIGHT: 35 kg per m². Lighter than many other roofing solutions, shingles allow a reduction in the size of your timber frame & joists.
Qualities
The expected lifespan of a Larch shingle roof is 30 to 40 years minimum, thus comparable to tiled & slate rooves.
Aesthetically a shingle roof blends in well with the landscape.
Weather resistance: larch shingles have a high resistance to rain, snow and frost. With their two attachment points the shingles offer a high resistance to strong winds & by partially overlapping each other, they are further protected from gales.
During the storms of December 1999 none of our roof shingles suffered any damage.
Order & Delivery
The boards of 2.50 m are delivered in secured piles with spacers & measure approximately 1.10 m wide & 1.20 m high. Depending on your chosen width, a pile equates to 85 m² to 90 m² of roof coverage.
The shingles can be cut on site to the desired length. Generally you will opt for a cut in 3 lengths of about 80 cm to maximise the yield & speed of pose. It is however possible to cut shingles to varying sizes to create a desired effect. The use of spacers ensures that piles can be moved with a fork lift after cutting into lengths
If you prefer we can cut your order into stacks of 83 cm long shingles.
Installation
Roof slope: the laying of a Larch shingle roof requires a roof pitch of 7/12 (30° or 58%). The steeper the slope the longer the life of the shingles will be increased.
Calculating Area & Length: the margin (le pureau) is the uncovered visible area or each shingle. It represents, in general, a third of the total surface of a shingle. We suggest a margin of about 30 cm & thus our 2.50m boards should be cut into 3 lengths of approximately 80 cm.
Shorter or longer margins can be employed by cutting shingles to 60cm or 120 cm.
The coefficient of roof area to shingle area varies with the complexity of the roof. Generally, it will be 2.8, but can rise in some cases to more than 3.
Example: for coverage of 120 m², this equates to 120 x 2.8 = 336 m² shingles.
For the 2AB battens/laths the coefficient is 3.5 for a simple roof with a margin of 30 cm. It can grow up to 5 for a more complex roof.
Example: coverage of 120 m², equates to 120 x 3.5 = 420 ml 2AB battens.
Weatherproof Membrane: As for any other type of roofing (tile, slate ...), it is essential to install an underlay before laying the shingles. The underlay prevents moisture infiltration (in case of powdery snow or penetrating fog, for example). The recommended underlays are listed below from the most to the least eco-friendly ( Microporous reinforced waterproof waxed cardboard, Wood fibre panel (type Isotoit), Roofing felt, Microporous reinforced plastic). Ambiance Bois strongly recommends the use of 35mm Isotoit wood fibre board which contributes generously to the insulation of your roof.
Installation is fast & efficient enabling the building to be watertight within a short time without the need for tarpaulin covers. Once in place the underlay cover must be completely waterproof. It is secured with laths/battens (type 16 x 50 mm dry sawn standard or 16 x 65 mm fresh heartwood) on each rafter.
2AB installation system: our Larch shingles are designed to be installed with our patented 2AB batten system. This system is unique to Ambiance Bois Limousin & ensures the circulation of air around the shingle.
2AB battens: the unique characteristic of the 2AB batten is the groove which holds the head of each shingle. The batten measures are 36 mm by 48 mm & come in lengths of 2 m, 2.40 m or 2.50 m.
The spacing between the rafters is expected to correspond to the width of the insulation in the roof space within an upper limit of 60 cm centres (this corresponds to the maximum resistance of 2AB battens.
The 2AB battens are fixed perpendicular to the rafters and vertical battens with galvanized 100 mm nails with the groove facing towards the eaves. Start at the bottom of the roof & work towards the ridge tracing the first row of battens 10 cm from the bottom of the rafters.
Measure the length of the roof between this batten and the ridge, eg. 10 m / Divide this by the length of the desired shingle margin i.e.30 cm: 10 / 0.30 = 33.33 / Round to the nearest whole number i.e. 33 giving you the number 2AB battens needed / Divide the length of the slope (10 m) by the number of battens cleats (33): 10/33 = 0.30 m, et voila you have the distance between each row of battens.
You can use the battens to enable you to move around the roof.
The shingle: Once all the battens are fixed in place the larch shingles can be placed in them, row after row working upwards from the bottom of the roof.
Larch shingles in the first row do not have a margin and thus should be cut shorter.
It is important to stagger each row so that the sides of each shingle are always offset by at least 3 cm compared to shingle in the row below.
The heartwood of each shingle should be orientated face down towards the roof. This takes advantage of the tendency of the shingle to deform & curl during drying aiding the evacuation of water from the roof.
Finally, as a precaution when laying in very dry weather, leave a space of 3 to 5 mm between each adjacent shingle to allow for expansion during periods of high humidity.
Two anchor points: Dual attachment ensures excellent support for the larch shingles. The nails should be stainless steel for maximum life & to prevent rust streaks on the roof.
-The top of the shingle is held in the groove of the batten
- 30 cm lower, the shingle is nailed to the 2AB batten below.
107 mm shingles are fixed with a single nail in the middle of the shingle. This requires 35 nails / m².
160 and 134 mm shingles are fixed with two nails about 2 cm from each edge. This requires 45 nails / m².
The shingles at the perimeter of the roof should be fixed with two nails as for the larger shingles.
Laying the hip: The hips & ridge of the roof requires additional attention in order to create a reliable seal against the weather. You must install stainless steel or copper flashing bent at the point of intersection and arranged in the same manner as the larch shingles (fig.3). The flashings are fixed with stainless steel nails.
Whenever a flashing attached lay the row of shingles adjacent to it. At the hip, shingles are fixed as elsewhere with just two precautions:
- They are cut so as to precisely follow the angle of the hip of the roof,
- Take care to select the widest shingles for the hip which will ensure sufficient width to nail the shingle to the battens
N.B. The shingles which are cut on an angle to follow the line of the hip cannot be lodged in the groove of the 2AB batten. Fixed with a single nail would mean that they could move in the wind & therefore you must secure the top of this shingle to the top of the adjacent shingles. This can be done by screwing a thinner piece of wood underneath the shingles near to their head prior to installation, ensuring that this thin batten does not prevent the adjacent single from sitting securely in the 2AB batten.
Laying the valleys: Similar precautions as those taken for laying of a hip to be taken to lay the valleys (Figure 4):
- Installation of flashings embedded in the 2AB batten and attached to the vertical batten beneath
- Cutting of shingles precisely at the same angle as the valley leaving a gap of about 10 cm between the two slopes of the roof.
Other cases: Connections to chimney stacks, pipe penetrations, skylights, etc ... are treated according to the same principles as the hips and valleys. Care should be taken to adapt the general rules that have been given to each situation which are designed to ensure maximum weatherproofing.
For roof windows: during installation of skylights (Velux type) fit connections supplied for non-flush flat roof mounting (slate type). Remember to fit a 2AB batten at the bottom of the skylight, which will aid the installation of the weather seal strips.
The Ridge: Attach the ridge flashing ( zinc, stainless steel or copper) with nails or screws that will reach the ridge board or a ledger installed at the tip of the rafters (15 to 25 cm depending on the roof pitch and the thickness of insulation).
The Lignolet Ridge is a more aesthetic solution achieved by overlapping the final row of shingles on the windward side of the ridge. This shingle will be nailed to the final 2AB batten. Before laying the Lignolet it is necessary to install a batten, which has the same thickness as the upper edge of the 2AB batten, below the penultimate shingle. This maintains the airflow beneath the shingle (refer to the schema above).
Wood Treatment
Larch heartwood is naturally resistant without any treatment to the level of class 3 for exterior use (Cf No. DTU 31.2 - reference AFNOR DTU P21-204 - NF EN 335). Once the larch shingles are installed, no finishing is needed: over time the roof will take on a silver-gray hue, without compromising its durability.
This advice sheet is indicative and not contractual. For normative reference on larch shingles, refer to the DTU 31.2 (Construction of houses and timber framed buildings) and DTU 41.2 (Exterior Cladding Wood).
