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Roofing

RE SLATE OF ROOF - BEST WAY TO MEET INSUALTION REQUIREMENTS

Anonymous user 03/03/2024 - 3.21 PM

My daughter has a 1950's built house where the roof is slated but does not have a membrane. Her intention is to have the roof stripped and a membrane fitted before re slating. The loft space is currently boarded at the highest portion i.e roof beam to purlin area. There is minimal insulation at the joists, however rockwool batts have been placed into the rather space (rafters about 100mm deep). The loft is only to be used for the occassional storeage of items such as suitcases etc. She recognises that there is a need, when the roof is re slated, to introduce sufficient insualtion to give a U-Value of 0.16. Rather than attempting to insualate into and over the rafters, could she have rigid board (Kingspan, Celotex with moisture layer 150mm thickness) fitted over her existing boarded area of the loft, then boarded over with sufficiently thick ply or wood composite floor boards ... then re use the rockwool batts at the eaves side of the oft space over the exposed joists to a thickness that meets the required U-Value? Any suggestions as to the best way forward to meet Building Control insualtion requirements would also be welcom. Thank you

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2 Answers

D&E Designs

Rating: 5 out of 5

Ormskirk

Hi, the Regulations are if the loft is an unheated space then the insulation must be placed at ceiling joist level. The insulation should ideally sit between and over the ceiling joists in 2 150mm layers, one between joists and one layer over in the other direction. You can then fit a stilt to form a raised storage platform over the insulation as it is import to not squash the insulation. Using Kingspan as you've indicated would be possible however it would be more expensive to do so.

Answered13 February 2019

A&G Projects

Rating: 4.7 out of 5

Christchurch

You certainly can use a rigid PIR insulation as you’ve suggested, but it’s an expensive material. Generally in this situation we would insulate between the existing ceiling joists with loft roll and then again over the joists to achieve the necessary U-value. If some or all of the loft is to be used as storage then we will install new timbers above the existing joists to raise the height (in order to accommodate the additional insulation) prior to boarding that section.

Answered17 February 2019