Installing Loft Vents

[MildlyIncompetent]

Hi all,

I've got an 1850's-ish semi which currently has no ventilation into the loft space, this was raised as a concern on the survey when we got the place.
Not noticed any moisture buildup in the loft space (not that I tend to spend much time looking up there..) but as I'm about to remove and replace the existing insulation and partially board it would this be a good time to pull back the insulation slightly from the edges and put in circular soffit vents?
There's no pipework or water tank in the loft, just the brick chimney running through the centre (in-use with a new steel flue), also having the loft treated for woodworm as there's historic and some current activity, not enough to cause structural issues though.

If I do install them, would it best to put them along all three sides or just front and back? Also are soffit vents enough or would it also really need a vent at the top of the roof?

 

[Leofric]

What area of ventilation per metre run do the proposed soffit vents allow ?
Ridge ventilation is recommended for steeper pitched roofs .
You need to allow a 50mm unobstructed air gap over the insulation at the eaves.

 

[MildlyIncompetent]

I'm looking at the 70mm circular vents, one place states it as "10,000mm2 per metre ventilation area at 200mm centres".
Not sure of the roof angle I'm afraid, but it doesn't look very steep to my uneducated eye.