Loft insulation. Warm loft, colder bedrooms?

[kp7722]

Hi,

I've recently moved into a 30 year old house which current has a warm loft. The insulation is up against the roof with plasterboard keeping it put. I understand that there needs to be a gap between the insulation and the roof felt and I have no reason to suspect that this wasn't done. There is no insulation in the loft floor. There are also no vents in the eaves which I presume is correct when having a warm loft.

My question is how much heat is lost from the bedrooms into the warm loft? And is it very ineffecient to have a warm loft if I only store things up there? We want to keep storing items in the loft but at the same time keep the heat in the bedrooms. Should I insulate in the loft floor as well or will this cause me problems with condensation, etc. What is recommended for this situation? If I insulate the loft floor do I need to remove the insulation in the roof and add some vents in the eaves, therefore converting it into a cold loft? Could I just add some 100mm/170mm thickness insulation in the loft floor to allow some heat to stay in the room and allow some heat into the loft?

Many thanks in advance, Paul.

[A.Clews]

Thus spake [e-mail] ( [e-mail]) unto the assembled multitudes:

I often think that fixing insulation under the roof itself is a waste of time, though perhaps it might help keep the loft cooler on a hot summer's day. To stop heat leaking into the loft from the rooms below, you need to insulate the loft floor. I don't think you need remove the existing roof insulation, but any heat getting into the loft is obviously wasting energy and money.

I laid floorboards in my loft, having laid insulation between the joists first and fixed wooden spacers on top of the joists to improve ventilation between the insulation and the floorboards.

I've measured temperatures of just below 0C in my loft on a cold winter's night, and as high as about 45C in high summer.

[terry]

Based on practice here the OP seems to be on the right track. Would add caveat that if you insulate ceiling it would be most desirable to have a vapor barrier on the 'warm' side of the insulation. Some claim that several coats of good 'oil' paint will act as an effective vapour barrier! Not sure about that being as effective as a polyethylene one? Once you have the bedrooms insulated from the attic some warmth and moisture will still escape up there and the attic being cooler than it is now should be watched carefully for condensation. And it may be necessary to to add or increase ventilation to avoid moisture, mould and rot up there to contents and structure. Necessary in my opinion even though the roof is insulated. The rule here is that there should be 0.3% (that's 3 sq feet say for every 1000 sq.feet of area) of ventilation in unheated attics and that it must be arranged to allow cross-ventilation. Eastern Canada; which is probably similar but somewaht cooler than say Northern Scotland, although we are at the same latitude as Spain!.