Ceiling insulation in sunroom
arnoldk
| Posted in General Questions on
Hi,
The current sunroom doesn’t have any insulation in the cathedral ceiling at the moment. The sunroom have three sides full of windows with an R-12 insulation in the 20 inches wall that those windows sit on. My wife wants to put an R-40 because she would like to keep the sunroom at 10*C (50*F) during the colder month but I’m don’t think it’s worth the cost given all of the windows.
Without doing an energy model, what would the maximum r-value that would be logical sense in my situation?
Thank you,
Arnold
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Replies
Simply put changing the ceiling will have almost no affect when the wall are single pane glass with an R value of 1. If the heat loss thru the glass is 3000 BTUs does it matter if the ceiling looses 300 or 3 BTUs it is almost a rounding error.
The smart move is to not heat the room with glass walls but it sounds like that battle is lost.
Walta
Hi Walta,
My wife wants to be able to keep the wet, snowy and dirty boots with the outdoor wear (especially from the kids) in sunroom during the colder months. She may change her mind if the hydro bill increases by to much.
The windows are double pane windows which are less than a year old so I suspect they're around an R-3 to R-4, still nothing to rave about like more windows. As for the ceiling insulation, are you recommending to not installing any insulation or vapour barrier in the ceiling before installing the tongue and groove pine wood ceiling ?
Thank you,
Arnold
Arnold,
What can you get into the rafters leaving room for a vent space? The relatively low cost of thicker batts for a single room means the penalty for going above what might make sense if you did energy modelling is minimal.
Hi Taylor,
I can install up to 12 inches of insulation and still leave 2-3 inches ventilation space. An R-40 fiberglass batt is 11 inches thick.
Thanks,
Arnold
Arnold,
We often see a succession of renovations where covered porches are enclosed to become three season sun-rooms, and later get conditioned as part of the living spaces. It seems like a good idea to me to bring some of the building. - like the roof and floor - up to code levels of insulation and air-sealing in anticipation of these possible later changes. Having that done means the additional work necessary if at some point the walls are altered to have less windows seems makes things a lot easier down the road.
If the ceiling is currently finished and seems to be working for you I would l would not do anything.
If the ceiling has been removed already. You need to be carful not to make it into a problem. It is all to easy for a cathedral ceiling to become a rotten moldy mess.
If the ceiling had been working for you, I would try to put it back the way it was.
In my mind air sealing is the most important step and T&G wood will not provide an adequate air barrier so you will need to add one.
If you said what climate zone you are in, I missed it.
If the choice is divorce or insulate the ceiling. LOL Read this article and pick the one that is best for your situation.
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
Get whatever R value you can fit without lowering the ceiling to much.
Walta
Thanks Walta and I'm in climate zone 6.
Luckily the ceiling isn't finished and I have full access to the scissor truss to add insulation and a vapour barrier before installing the T&G wood ceiling.
Thanks,
Arnold
Arnold,
Go for it, the room will be much warmer with the ceiling insulated. I have done similar work on a Minneapolis sunroom. Upgraded the windows to thermopane and added rigid to the previously uninsulated ceiling. The sunroom warms up nicely during the day, this is the room where the owner puts the dogs out, so it is busy. If you are looking for quality information on cold climate building, talk to someone adept who builds in a cold climate.
Doug
> Go for it, the room will be much warmer with the ceiling insulated.
I can see air sealing doing a bit to prevent convective heat loss, but how will insulation help in room with glass on 3 sides? Any passive solar gain is going to radiate out of those windows quickly at nightfall, as will any heat provided by the HVAC system.
Anything will help, but how much difference you'll see depends entirely on how large the area you're insulating is compared to the area of the glazing. If you have a lean-to type sunroom with a few feet of roof overhang before the glass (a "soffit's width", for example), then you probably won't see much difference in the room temperature when you upgrade the insulation in that relatively small area of roof. If the roof area is large, with a relatively small area of glass, such as maybe a sunroom at the end of a long hallway (hard to think of a good example for this one), then the much larger area of roof insulation would make a bigger difference.
If you have only 10% or so of the total area of the room being insulated, then I wouldn't expect to notice much difference bumping up the insulation R value a bit. I would check if there is any air sealing that can be done, and upping the insulation won't hurt, but you'd have to decide if it's worth the effort to do the installation.
Bill
Arnold is not going to turn this room into a bedroom, just make it more comfortable than it currently is. I am assuming the usage would be in the daylight hours and if sunny will be quite comfortable.
Some years ago, MN building code would not allow a 3 or 4 season room to be connected to the main heating source. The room had to meet the energy code as a stand-alone room and they never did due to all of the glass. Also, there had to be an exterior door between the rooms. The code has since changed.
"Without doing an energy model, what would the maximum r-value that would be logical sense in my situation?"
That's like asking, "without using a tape measure, will these pants fit me?" You're just not going to get a sensible answer. It's not hard to do a simple, back-of-the-envelope energy model. Heat loss through a surface, in BTU per hour, is equal to the surface area in square feet times the temperature difference between the two sides, divided by the R-value.
Get the dimensions of all of the exterior surfaces of this room -- walls, floor, roof. Find your average January/February temperature, and use that to calculate the average winter heating load, in BTU/hr, for each surface. Add them up to get the load for the room. Then you have to figure out how many hours of heating to expect per season. Find the seasonal heating degree-days for your location, on the internet. Multiply by 24 to get degree-hours. Divide by the difference between 65F and your average winter temperature that you used earlier, to get heating hours.
Multiply heating hours by the BTU per hour you calculated to get BTU per season. Then you have to figure out your cost per BTU, that depends on what type of heating system you have and how expensive the fuel for it is. From the cost per BTU and BTU per year you get an annual heating cost.
You run this at least twice, once for the current insulation level, again for the proposed new level. You can do it as many times as you like. It's also useful to break the cost down by surface, to see which ones contribute the most to the cost. For example, if the roof isn't a big source of cost right now, improving it may not be the best use of your time and money.
Then it's entirely up to you whether the increase in annual heating cost is worth the increase in comfort you'll experience.