Roof renovation needs to be prepared carefully. Observing the established rules will not harm the work, and roof replacement will certainly go more smoothly. Therefore, before we put new tiles on the roof, we need to check the condition of the rafter framing, roof sheathing and insulation. It is advisable to have an expert examination done to find out what can still be repaired, and what can only be replaced.
Before replacing a roof, the most important thing is to decide what the new roofing material should be. We look through catalogues and see what’s on neighbouring roofs. However, we should start from something completely different.
Repairing the roof trusses
The builder or engineer who will assess the roof trusses may recommend several treatments for them:
- strengthening the rafter framing – applying additional rafter and maypole supports or adding new rafters. This is a rather complicated procedure, which must be carried out by carpenters according to a previously prepared project. A simpler repair is to strengthen the rafters by welding them together on both sides with planks or stiffening the slope with steel bands, the so-called welts;
- fungicidal treatment of wood – house fungus can completely destroy the rafter framing. The intruder must be removed by specialists. Infected and adjacent sections must be removed. The rest of the rafter framing (including the mentioned parts) must be thoroughly impregnated with a fungicide;
- deworming – if the rafter framing is infested with pests, the infested sections must be replaced and the rest must be treated with a deworming agent;
- replacement of the roof framing – sometimes it is not economical to repair. Replace the roof trusses when the mould growth exceeds 20% or the roof is heavily infested with insect larvae. Similarly, when cracks, buckling and other structural defects cover more than 50% of the whole structure.
What’s beyond the rafter framing – how to prepare for roof repair
Precise measurements, visualisation of rafter framing, sheathing and insulation will allow us to calculate the amount of material necessary for the renovation. It is also worth ordering a container or a truck to take away the old roofing. We also need to protect the area around the house from possible damage.
The rest is up to roofers who will remove the covering, check the condition of insulation, level crooked slopes or replace the waterproofing material. They will also install new gutters or eaves flashings and gutter hooks. And all this will be done before the roofing is replaced.
On the other hand, before the roof renovation begins for good, we should prepare ourselves for weather surprises. Exposed wooden roof structure does not like rain – it is difficult to dry it. So it’s worth having a thick plastic tarpaulin at hand to protect the rafter framing against unexpected rainfall.
Roof replacement provides opportunity for loft insulation
Roof replacement is the ideal time to add thermal insulation to a poorly insulated roof. If we also want to adapt a previously unused attic, we will insulate it from the inside. Then an additional layer of thermal insulation material will be placed between and under rafters, before bevels and walls are covered with finishing cladding.
However, if we do not want to demolish the finished attic, we can insulate the roof from the outside when replacing the roofing. If it has a rigid sheathing, we can lay on it thermo-insulating boards made of hard and non-absorbable material, e.g. polyurethane PIR or extruded polystyrene XPS. On such thermal insulation layer, which is usually 5-10 cm thick, a load-bearing grid for future roofing is installed.
If, however, there is the initial covering foil, it is best to remove it, nail thick counter-battens to the rafters, place additional insulation between them and install the remaining layers of the roof together with the foil. Of course, it is also possible to build new, rigid sheathing. The disadvantage of insulating the roof from the outside is that the slope thickness increases significantly. It requires the use of various non-standard products and non-standard solutions, especially when it comes to flashings and finishing of ridges, corners and roof eaves.
It will be easiest to insulate an unutilised attic, because the thermal insulation material will not be laid in the slope, but on the ceiling above the last storey. This work can be carried out at any time because it is not connected with roof renovation.
Will the old sheathing support the new roofing?
The load-bearing structure of the old roofing may be counter-battens and battens cut across them or rigid sheathing, usually insulated with roofing felt. Often both types of structure function simultaneously. Our roofers are best placed to assess whether the new roofing can be installed on the old substructure. As a rule, they decide to remove it, as it is easier for them to install the covering from scratch. The type of new substructure will depend primarily on the type of roofing chosen.
Rigid sheathing made of boards or wood-based panels is only necessary for roofing made of asphalt shingles, wood chips, slate or flat metal sheets. All profiled types of roofing (tiles, sheet tiles, corrugated sheets) are fastened to a grid of battens and counter-battens.
Such a grid, if we choose the highly vapour-permeable foil for water insulation, is installed directly on rafters. If, on the other hand, the insulation is made of roofing paper, rigid sheathing will be needed under the grid and under it. The version with the foil is favourable due to the fact that it is easier to ventilate the roof slope. The foil lets the vapour through from the loft side. The rigid sheathing additionally stiffens the rafter framing and improves the sound insulation of the roof. Together with roofing paper it is also a cheaper alternative for the expensive foil. Unfortunately, it weighs down the rafter framing considerably.
A roofer is worth his weight in gold. How to find a good expert?
Replacement of the roofing and all additional works that accompany it, should be done by a qualified roofing team. It is best to hire a recommended company or choose one via the Internet and look for opinions about it on discussion forums dedicated to construction. This is the best way for a successful verification. It is not worth saving on roofers. The best professionals know their worth and are not cheap. Remember to book a team well in advance, even before the season, that is in February or March. Some works, including installation of windows or skylights, can be done by ourselves, but it is better to commission them to professionals.