Stu68

Thanks for your replies, Im pretty sure that the loft is designed to be a warm roof as it is airtight inso much that the Actis is taped on all joins on the outside overlaps and there is no ventilation to the outside. Infact when we had the airtightness test done we had a result of 8.4, which was higher than we were expecting. The chap did a test on the attic space (using the fan on the loft hatch) and he said we weren't losing a lot through the roof and he said it was performing well, so I think the loft was/is intended to be a warm one. (we tracked down the leaks to elsewhere downstairs and then returned a result of 3), which were happy with considering the construction method. My main thought was, could i add extra insulation between the rafters (leaving a 25mm gap between Actis and insulation) and not create condensation? With my attic is 15 deg and the rooms 20, is there much benefit in me insulating the MVHR ducting that runs in the loft or trying to make the loft space warmer? Many thanks.Stuart

The Actis is taped on all joins but on the outside (ie. the slates side) however I can easily tape the inside as well. Thanks for the reply, its good to see others using the product!

Firstly, can I just thank you all for replying, I really do appreciate it and will take on board any advice given. After you replies I have tried to answer some of the points made as best as i can and taken some more measurements. The photos I hope will explain also. The roof space is purely used for storage as its 30m long I suppose a air rifle range would be the only option! To add the the mix, i think i was little optimistic in temp differences between rooms and loft space. Its icy outside and the interior rooms are 20deg C, the loft space is currently 15 Deg.C. You will see that in places (Hall) there is a vaulted ceiling which only differ inso much that there is rockwell 100mm, between the roof rafters in that section of ceiling. The space blanket is Actis Triso Super 10+ Was sold this idea on the basis that is was so say the mutts nuts and the builder had extensive good experiences/ results when using it in the same way as my property. Didn't help that my building inspector seemed to agree! I am happy to consider putting rigid celotex between the roof rafters or mineral wool if you guys think it will make a worthwhile improvement too. I was thinking that the ceiling joist wool, was actually trapping heat in the rooms downstairs and preventing the roof space to warm up and become constant temperature. Is this likely to be the case or is the main reason for the temp difference heat loss through the roof? I suppose I am still unsure if my roof is a warm or cold or a hybrid, in which case how best to approach things. Many thanks for thing the time to reply. Regards stuart Hope these pics help show you what's what.

Our build (4 ears old) is of reasonable airtightness (approx 3.2 in the airtightness test). Our contractor left us in the lurch before completing our 3500sqft home, leaving us to complete it ourselves using 3rd parties. I am trying to improve the overall insulation performance and am being given differing views what's best. We have GSHP, and MVHR. The contractor advised me that we have a "warm roof" which I understand, and consists of Foil space blanket, over the rafters forming an airtight loft space. My issue is: Currently we have, 170mm rock wool insulation between the ceiling joists in the loft space which has for the majority then been boarded with chipboard flooring. There is no added insulation between the roof joists (i can see the underside of the space blanket). All the MVHR ducting is exposed in this "warm " loft space and I was told it doesn't need any further duct insulation as it sits in aware loft? MVHR aside, the main thing is surely the Rockwool in the ceiling joists are counterproductive and is prevent heat rising into the 'warm" loft? I am looking for something assuring of if it is best for me to remove the rock wool from the ceiling joists (which means taking up the boards as well), and putting that insulation (or new insulation) between the roof rafters (180mm of joist depth spare). Some builders have said " waste of time". just add new rock wool type insulation between the row joists to enhance the space blankets effectiveness, others are telling me exactly the opposite, that my loft won't be as warm as it should be with the ceiling rock wool in place, and my MVHR is suffering as a result. Lastly yet another contractor told us that its fine as it is and we should just insulate the MVHR ducting. The temp in the loft space in the winter is typically a few 1-2 degrees lower than the rooms below. Is there a definitive correct answer here as to how I should proceed ? I have included a pic of the house and its mainly the long single story section I am referring to.