How many people have been told this by their builder? I’m afraid it’s not quite true. The purpose of the NHBC Buildmark warranty is to hold the builder to account in case their work does not meet the NHBC requirements – a strict set of standards which are based on building regulations.
In a nutshell, during the first two years after completion the builder is responsible for rectifying any failures to meet the standard. In the 3-10 years after completion the NHBC just provides insurance for damage that is a direct result of such a failure, and they will pay out for your claim in such cases.
So in the event that you have a problem with your house the NHBC would need to ascertain who was to blame for the damage – was it the builder who didn’t meet requirements? Or is it a result of something you have done to the property whilst the builder’s work is satisfactory?
It would be difficult for the builder to blame loft boarding for ANY issue you have with your house, rendering your warranty ‘void’. There is no text in the Buildmark policy that gives the NHBC a blanket ‘out’ like this. See for yourself: http://www.nhbc.co.uk/Homeowners/Findyourpolicydocument/
In the case of loft flooring, the damage could really be one of 2 main things:
A roof space is designed for condensation to form and then be removed by suitable airflow to the outside environment. The builder will argue that the boards have restricted the airflow and prevented the condensation from being ventilated away. All you need to do is show the BBA report proving that when installed correctly, LoftZone does not affect this airflow because it leaves a suitable gap. See the report here: http://www.bbacerts.co.uk/CertificateFiles/52/5269PS1i1.pdf
British Standards require that the design of your roof trusses can accommodate a minimum static load of 25kg per sqm for storage PLUS a dynamic point load of 180kg at the weakest point. If they are not strong enough or you exceed this amount then you may see nail pops in the ceiling plasterboard from the joist movement… Or worse.
What does this mean for you?
There are only two things you need to do to prevent the NHBC from weaseling out of a valid claim – choose a loft boarding product which has been independently verified to support building regs and not store more than 25kgs per sqm in your loft.
So in summary:
whilst flooring your loft cannot void your whole house warranty, doing it the wrong way CAN result in you missing out on a claim for certain loft specific issues.