Often, each of us is tempted to choose the lowest price offer, without really comparing multiple offers.
The first selection should be based on the type or types of the roof you choose. Analyze the offer and ask what it contains.
Before the final decision, ask for the documents certifying the quality of the product: the declaration of conformity (CE), the warranty certificate, the technical sheet. The products must contain the traceability of the product (product name, country of origin, processing date / batch number, CE mark on the back or on the packaging label). Sometimes, the products supplied are not the original products. Do not hesitate to contact the manufacturer or importer to make sure you receive the original.
When signing the contract, do not hesitate to enter as a clause, that the roofer should assum any additional costs over 3-5%. The estimation cost is the exclusive result of the roofer, which is why it is not justified to pay extra fees in case there are no changes generated by you. Failure to comply with the plan quotas, when the roof is made, can not be assumed by the roofer. In such case, simply request a recalculation of the offer before delivery.
Based on this analysis, you will decide at least about the type of roof, model and color.
To choose the distributor you will work with, make sure it has specialized installers or trained partners. Ask them to show you at least one completed roof. It is preferable to avoid installers without reference or with a much lower cost of work. Ask for both warranty for materials and installation. This way you can stay assured that you have received all the materials from the offer, and also discourage "occasional installers."
There are two large categories of roofing membranes that ensure the long-term efficiency of the insulation: inside, a vapor barrier and outside, an anti-condensation foil. The vapor barrier is designed to prevent the air from flowing outdoors and to limit the amount of vapor transported outwards. Anti- condensation foil allows the vapor that reaches the thermal insulation layer to exit as quickly as possible and prevents formation of condensation that would affect thermal insulation. At the same time, it prevents condensation, which can form under the roof, from entering the thermal insulation layer.
In order to choose the right type of membrane to protect your roof, you need to consider a number of criteria: vapor permeability (Sd value), type of roof (with hardboarding / without hardboarding, ventilated/ unventilated, uninhabited, roofing type (ceramic, concrete, metal, other types ...).