Increasing the depth of rafters

Hi first of all you need to determine what kind of felt is on the roof so ….. a modern breathable membrane felt requires a 25mm air gap but An old none breathable felt actually requires a 50mm air flow from the felt to insulating board. This is the most important part before anything else the amount of jobs I go to and people have only left a 25 mm air gap for a none breathable felt is unbelievable the condensation is unreal and in most cases people actually think there roof is leaking. So please check the felt on the roof if any before anything else. Example. So if we where putting 100 mm kingspan insulation boards between joists we would need to stitch 125mm or greater timbers to the existing joists for the correct air flow. If it’s none breathable membrane we would stitch 150mm timber to the existing joists. Also we would always stitch to the side and never directly on the face reason been ….. If you where planning to plaster board and skim stitching straight on the face of the old joist can result in problems if the joists are not running plum with one another. Using the stitching technique you can make sure everything is running plum with one another. Hope this helps

Hello simple way is to screw timber directly on too the old timber to create a deeper void for insulation but remember you will need 25mm behind the insulation as well for air flow I hope this helps

Hi this is something I have come across numerous times and is easily sorted. You can fix timber over the existing rafters to make the required depth. Make sure the insulation goes right up the eaves and there no gaps. Also make sure the insulation is not compressed or it will lose some of its insulation properties. Leave at least an inch above the insulation for air flow if you are going to board over it. One last thing I don't recommend the fibreglass insulation as it's quite nasty to use. Most big stores now stock a similar insulation but without the fibreglass. B & q do a recycled plastic insulation which is really good and easy to use and you won't be itching for days after doing it.