loft insulation & vents in eaves issue...

LoadZaFunk

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Hi & thanks for taking the time to review my issue...

Current issue:
Air vents in eaves both sides of a double height extension 5m long either side. This causes outside sound to be heard in the bedroom as if the double glazing is open plus the room being 2-3 degrees cooler than the rest of the house.

Current insulation:
Ceiling is silver backed (loft side) & joist width & depth insulation roll. Each roll does not go as far as the crossing point of the pitched roof rafters & ceiling joists @eaves. Daylight from the air vents is visible at each side of the loft, the gap where the light is visible is about 20cm along both sides running 5m. There is no visible insulation on the roof, loft hatch or above the downlighters.

Solution I'd like to achieve:
Keep the ventilation to avoid condensation.
Sound proof the outside noise.
Thermally insulate the loft ensuring the bedroom is kept the same temperature as the rest of the house plus the loft space is kept insulated for storage.

How?:
How do I check the thickness of the current insulation? How do you measure material which squashes flat?
How much ventilation is required for a loft? Considering 2x 5m is currently installed. How much can I reduce this by?
How can I minimise the daylight in the loft? Should the insulation from the roof overlap the ceiling insulation?
How should I insulate brickwork in the loft?

All answers gratefully received...

brig001

I'm struggling to visualise exactly what you mean, but as a rule 50mm (2 inches) gap should be left between the roofing felt and the loft insulation for ventilation, so it can be moved around to suit and any gaps filled in.

To be honest though, I would bet that the biggest problem you have is the downlighters. These need to be covered by either a loftcap like this: http://www.allaboutelectrics.co.uk/aico-thermal-loft-cap.html or a plasterboard box made big enough so that you can insulate on top of it. See Lucia Fermi's post on this: http://www.screwfix.com/talk/thread.jspa?threadID=72755&messageID=1084203 . The best solution ould be to get rid of the downlighters, repair the ceiling to its original state and get something else instead. Then you can pile all the insulation you like on top which will kill the sound considerably.
HTH, Brian.

WestonDave

Chances are if the insulations only comes up to joist level then you've only got 100mm. Easiest way to measure it is to measure the joist height - given that insulation rolls tend to come in standard thicknesses (100, 150 and 170mm) you'll be fine working out which is the nearest of those. If you've only got 100, then ideally you want another 170mm on top, preferably at right angles to the original to avoid cold spots from the joists. That however will make the loft unusable for storage as you can't crush the insulation and still have it effective. The alternative (assuming you have 100mm between the joists) is to use two layers of space board type insulation to give you the right equivalent insulation, and then put floor panels over the top. Insulating the roof to keep the storage area warm is a waste of time - you don't need to heat that space so you are better keeping the warmth in the house.

For the downlights use as above, or Screwfix do some metal boxes you can use for the same purpose - (the idea is to keep the insulation fibres out of the lights and create an air gap around them to stop them overheating.)

The additional insulation or boarding will help with the sound effects. Daylight entering into the loft isn't an issue you need to resolve, and I personally wouldn't be cutting down on ventilation especially if you are increasing the insulation as this will make the loft space colder so it will need more airflow to avoid condensation.

If you go the space board route, you'll probably end up with a couple of offcuts - stick these to the loft side of the loft hatch to improve insulation on that - maybe think about some brush type draught excluders around the edge to avoid airflow.