A quality installation begins with proper sub-floor preparation and not all products require the same level of perfection. When installing floating floors, including laminate, engineered and click together vinyl plank, the sub-floor should be solid, clean, squeak free, dry, and flat within the manufacturer’s specifications.
The tolerance for flatness will depend on the type of material being installed as well as the type of underlay being used. Thinner vinyl planks that already have an underlay attached, are referred to as “pad attached” and may require the highest level of accuracy in terms of flatness. Due to the pliability of the thinner vinyl planks, it is important to ensure the sub-floor is free of any undulations, which could affect the integrity of the locking system. Most pad attached flooring products do not allow the use of an additional underlay, as it may cause too much deflection, which could cause the product to come apart. It is also important to note that the attached pads do not usually cover and support the joints of the locking system which further reinforces the need for the higher standard of sub-floor preparation when selecting this type of product.
Laminate and engineered hardwood floors are usually thicker than vinyl and therefore more rigid, allowing for more product deflection. This increased rigidity provides for more options when selecting the underlay to be used. Better quality underlays can make a noticeable difference in the overall comfort and performance of a floating floor. For the installation of laminate and engineered 
floors we recommend using the best underlay possible and our most popular choice is Ultra Felt, which is a 3 mm fabric type of underlay. Ultra Felt helps to mask minor imperfections in the sub-floor, as well as providing better underfoot comfort, noise reduction and increased warmth.
Fixing your sub-floor problems
Potential sub-floor issues can only be determined once the existing flooring has been removed and the area has been thoroughly cleaned. Each installation area should be independently checked and you should never assume that because one room is flat and level that all rooms are the same. 
It also doesn’t matter if your sub-floor is concrete or plywood. High spots in a concrete sub-floor can be reduced with a concrete grinder and wood sub-floors can be fixed by sanding or planning the area to the desired height.
A large hump in a plywood sub-floor, may be caused by a joist that is crowned the wrong way. In extreme cases it may be necessary to remove the plywood in order to shave down the joist(s) and then re-install the plywood. 
Low spots or dips in the sub-floor can be fixed with an approved levelling compound that is mixed and poured in the area and then feathered on the edges to match the height of the surrounding area. Once dried, the area can be sanded further to the meet the level of flatness required for the product being installed. For questions regarding sub-floor issues please contact laminatewarehouse@shaw.ca
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