Member
· Västra Götaland
· 1 709 posts
I think insulation takes precedence over ceiling height. In similar constructions, I usually lower the ceiling height downstairs and have the patio door upstairs positioned 15 cm higher than the interior floor. Stepping up 15 cm is not seen as unusual there.
Both SP and even I (!) believe that it is possible to skip the air gap in the roof if done correctly today. This requires a lot of insulation, e.g., 400 mm ecowool, a vapor barrier installed CAREFULLY, and a roofing material with less vapor resistance than plastic. For example, Protan roofing membrane. That's what I think you should do. The rafters slope at LEAST 1:20 at the top, then the deck joists should be tapered to achieve a flat deck floor. No joists are screwed through the roofing membrane, it stays put anyway. If concerned, you can attach the entire deck framework to the house wall on the inner edge. The deck joists should be made minimally high on the inner edge to reduce construction height. Maybe 40 mm, as long as you can screw the decking without reaching the roofing membrane.
Both SP and even I (!) believe that it is possible to skip the air gap in the roof if done correctly today. This requires a lot of insulation, e.g., 400 mm ecowool, a vapor barrier installed CAREFULLY, and a roofing material with less vapor resistance than plastic. For example, Protan roofing membrane. That's what I think you should do. The rafters slope at LEAST 1:20 at the top, then the deck joists should be tapered to achieve a flat deck floor. No joists are screwed through the roofing membrane, it stays put anyway. If concerned, you can attach the entire deck framework to the house wall on the inner edge. The deck joists should be made minimally high on the inner edge to reduce construction height. Maybe 40 mm, as long as you can screw the decking without reaching the roofing membrane.
The problem here is not that there is no desire to insulate but that the building permit submitted limits the heights. As I understand it, TS would like to solve the problem without having to change the building permit since the municipality is a bit nitpicky and it will take time and cost more.
I think that the original poster should have a discussion with the municipality about what it would mean to make some changes to the building permit. It shouldn't result in a full fee again. As I see it, it's not possible to achieve a good solution with the current conditions. It's better to pay a little more for the building permit than to spend large amounts on something that won't turn out well. I am quite sure that it will look better with a slightly recessed extension, in addition to all the benefits of dimensions and insulation. If the building permit officer doesn't buy that argument, then speak with the city architect.
Yes, the building permit is the primary problem now; they don't seem keen on deviations. But I will try to get a concrete answer on how I can make changes and what the process is around that.
Regarding the extension's height, and indirectly the thickness of the floor joists, it is desirable from several other aspects to keep the building height down. Since the terrace's railings are to be hidden behind the gable, every cm I raise the terrace's floor level also means that the terrace's width must decrease by almost 2 cm on each side. A height increase of 15 cm thus reduces the terrace by 2.5 sqm.
Moreover, the door that (at a later stage) is to be installed from the attic will appear even more like dwarf size. And last but not least, the assessment of privacy to neighbors will be different if the roof is raised.
I understand, of course, that there will have to be some form of compromise; you can't have everything. But I still want to find the thinnest solution possible to make the smallest compromises. Compromises that I currently feel most willing to make are poorer insulation and reduced ceiling height. The latter is, of course, not at all certain the municipality will approve. Another option is to perhaps lower the floor height, thus having the extension and the house at different levels. I would preferably avoid this, but as I said, you can't always have everything.
Regarding the extension's height, and indirectly the thickness of the floor joists, it is desirable from several other aspects to keep the building height down. Since the terrace's railings are to be hidden behind the gable, every cm I raise the terrace's floor level also means that the terrace's width must decrease by almost 2 cm on each side. A height increase of 15 cm thus reduces the terrace by 2.5 sqm.
Moreover, the door that (at a later stage) is to be installed from the attic will appear even more like dwarf size. And last but not least, the assessment of privacy to neighbors will be different if the roof is raised.
I understand, of course, that there will have to be some form of compromise; you can't have everything. But I still want to find the thinnest solution possible to make the smallest compromises. Compromises that I currently feel most willing to make are poorer insulation and reduced ceiling height. The latter is, of course, not at all certain the municipality will approve. Another option is to perhaps lower the floor height, thus having the extension and the house at different levels. I would preferably avoid this, but as I said, you can't always have everything.
If I get the room height down to 2.3, manage to negotiate a few cm at the top, then I have just over 350mm to work with. If I then change so that the front support beam rests on four posts so it can be resized down and the beams from wood to steel, maybe it becomes feasible? What do you think? I can compromise on insulation (it's not going to winter here anyway 
), as well as a slope of perhaps 5-10cm.
I could also consider an additional support beam in the middle, but it wouldn't be able to have posts along the way, so the dimension would probably end up being like an HEB240, and maybe that won't help?
), as well as a slope of perhaps 5-10cm.I could also consider an additional support beam in the middle, but it wouldn't be able to have posts along the way, so the dimension would probably end up being like an HEB240, and maybe that won't help?
One option is to classify the room as a conservatory, which simplifies everything. However, this requires some other measures. Another possibility is to dig down a bit to increase the room height. The level difference that arises is OK considering accessibility standards.
Hm, classifying as a conservatory I will need to investigate.J justusandersson said:
Lowering the floor level can be done without digging; the current house is at a 30cm height, so just by placing the extension at ground level, you gain that much. And as I said, I understand that some compromise will probably be needed, but before I decide how much and which one, I would still like to figure out what the absolute thinnest flooring I can get away with...
Lowering the floor in the extension sounds like a good idea. It will also create a nicer transition between outside and inside, especially with such large sections. Personally, I would also want the roof in the existing house to meet the roof in the extension without a gap due to different ceiling heights. You could extend the extension's roof so that it meets the interior ceiling in the house. If you have erge-beam, you could also have the first step start inside the house, and you could achieve 2400mm in ceiling height all the way out. 350mm as the thinnest inside by the wall, without considering the decking, could probably be managed with koljern.J justusandersson said:
Yes, as mentioned, it is an option, but since the idea is that the dining room and kitchen should continue into the extension, it creates some limitations in furniture arrangement, etc. Something that can be lived with if a better compromise isn't found.B bossespecial said:
Regarding the notch in ceiling height, there will still be a steel beam to support the opening of the wall, so the "notch" will be there anyway...
Self-builder
· Arvika
· 1 527 posts
The beam parallel to the gable can be recessed into the ceiling, then I saw a shifting of the heart wall, this could also be fitted into the floor structure.
Self-builder
· Arvika
· 1 527 posts
As mentioned, everything can be solved, but it costs both time and money. I often try to see "extreme" solutions from the start so you can pick up things along the way, even if you ultimately choose a simpler solution. If you choose the simplest solution directly, you often miss out on a lot that you could have taken with you.
Member
· Blekinge
· 10 117 posts
Avoiding getting a notch in the ceiling is immensely valuable. I myself have an extension whose floor level is 80 cm lower but with the same ceiling level as the original house. The room height in the extension is therefore over three meters. A fantastic feeling when you stand on the stairs going down into the extension!
Self-builder
· Arvika
· 1 527 posts
Is the attic already furnished? Otherwise, one could lift a sturdy beam upwards in the wall and place the terrace on the underside flange. Additionally, one could further insulate the gable and account for the energy improvement in the extension. I also think it would be easier and yield a better result if one removed the entire gable wall and built new walls. There isn't much of the gable left, really.