I just finished add on enclosed patio 22' x16' 2ft high knee wall the rest is all glass.This is a shed roof design which comes off the back of the house.I have 2x10 joist and insulated it with 9" fiberglass. the question is people are telling me that I should not have done that because it will build up to much heat in the roof.I do have a 2' overhang that is non vented but enclosed with sofit. did I make a mistake? By the way I live in upstate NY where the winters get pretty cold.any suggestions? thanks Phil P.S This room is not heated except for a small heater to take the chill ouy.
You won't get anymore heat buildup in the roof if you did not insulate the ceiling, so what you have bene told is not correct.
And it would not matter if the rafters were not vented provided you do not heat the space. The reason is if the room is 3 season only, and not heated, then there will be no temperature/humidity differentials between the outside and inside and therefore no worries about condensation.
But the minute you condition the space either with heat or air conditioning you alter the equilibrium the room has with the exterior and the roof rafter spaces need to be ventilated from the eaves to the peak to prevent condensation.
Thanks for the reply. to clarify a little there is no peak it is a shed roof which connects to the side of the house.What they are saying is that in the summer it will build up to much heat on the roof and ruin the shingles.True or False?
Old wives tale. Would you rather have the heat IN your space? It's going to be hot enough as it is with so much glass, unless you've paid careful attention to ventilation of the space. Which direction is the room oriented toward? Is there shade nearby? What color are the shingles?
Architect (NY) and Home Designer (PA)
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005
There are 'ridge vents' available for shed roofs that attach as if they were flashing between the house and the highest slope of a shed roof.
I have seen them at Lowes and Home Depot.
They run the full width of the shed roof and use ventilated soffits for air intake and look like the older style metal ridge vents.
One might even make their own shed roof vent using a rolled Cobra vent placed over spaces left in the sheathing at the high point of a shed roof. The roll vent would need to be flashed over from under the siding of the attached house.
BUT with 9 inches of insulation in a 2x10, that leaves a nominal 1/4 inch for air flow, and practically speaking, that 1/4 inch is probably zero. I suppose a vent is better than no vent, but I still don't see a problem unless the room will be fully heated or conditioned in the future.
Architect (NY) and Home Designer (PA)
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005
I suppose a vent is better than no vent, but I still don't see a problem unless the room will be fully heated or conditioned in the future.
I agree and Philthy would have to use rafter vents from eave to 'peak' in order to get the shed-type ridge vent to work anyhow because of the lack of clear space between insulation and roof sheathing..
And since there will be no heating or cooling, no temperature differentials therefore no condensation worries....
Not sure that I agree that there will be no condensation in unconditioned space. I have corregated fiberglas shed type roof over wood deck with NO open sides but get condensation - to the point of drips during cool, damp weater. Perhaps due to heat/moisture loss from sliding glass doors into house underneath the roof. Was a surprise to me. I have not insulated since the sunlight through the fiberglas is desired more than the nuisance of occasional drips - but any solutions welcome! Thanks.
What we've proofed in Germany is that any lightweight thermal insulation can not stop the IR radiation which causes 99% of thermal flux through walls.
You can see it on the figure, all the lightweight materials get high temperature after 10 minutes shining of a red lamp bulb. So your roof should have been insulated by wood or gypsum card board or any other solid material to stop summer heat and winter cold.
The materials - all 4 cm thick - on the figure from above: fiberglass, polyfoam, foamglass, solid brick, wood fiber board, gypsum card board, solid pinewood. 'U-Wert' means R-value and is worth for nothing!
Originally posted by KonradFischer: What we've proofed in Germany is that any lightweight thermal insulation can not stop the IR radiation which causes 99% of thermal flux through walls.
It is definitely true that the building codes are effectively written by the insulation manufacturers in order to sell more information, with no regard for real energy conservation. But something doesn't make sense to me:
1. While IR does CAUSE the heat flux, isn't it converted into CONDUCTIVE heat flux by the elimination of any air spaces between the material that receives the IR and the actual insulation. So heat only passes through the assembly by IR if you use batt, because it's just a big air space anyways.
2. In hot climates, don't they use radiant barriers already? Even so, doesn't latent heat reduction requires more electricity than sensible heat reduction? Conductive & radiative performance are irrelevant for that aspect...
Our experiment (look to the figure) proves, that there is very few thermal flux in solid materials. So there can be nearly no conversion of IR in 'conductive' heat flux. And in which way shall conductive heat flux work? Which form of molecular transactions should transport the heat? And how will it be comparing with the experiment? I suppose, that conductive (similiar mechanically) heat transport will only happen for instance if warm air molecules will give their 'move-energy' (corresponding with their grade of temperature) in colder surface molecules of the wall - or an other example - if your warm hand will contact a room temperatured steel plate and a insulation board. There is the R-value and the hypothesis of conductivity valid, but not what belongs the transport inside the material. Otherwise I could not understand the results of our experiment.
I do not know what is your opinion about the difference between latent heat reduction and sensible heat reduction. To cool off a glass building with electrical vent is on long time more expensive than to have a solid envelope around the building, which can store warmth in winter and coolness in summer like the adobe buildings.
Isn't your experiment invalid if the insulations are never exposed to infrared heat in the field? Where insulation is sandwiched between OSB & drywall, there is no air space to enable radiative heat transfer.
For example, on a hot day, exterior sheathing (OSB) molecules are excited by IR (electromagnetic waves) emitted by the cladding. Mechanical action transmits the heat inward by conduction to the insulation. But the OSB is continually connected to the cellulose or foam plastic, etc. So the excited OSB molecules transmit via mechanical action to the insulation.
I realize that this is not a source of energy consumption in Germany, but in the US, the bulk of energy consumption comes from air leakage. In hot climates, they use decent SHGC and overhangs combined with tile roofs etc to reduce solar heat gain contributions.
And it doesn't take much humidity ingress to cause increased electricity usage. In America they use electrically powered air conditioners, and the electricity usage for dehumidification is ridiculously high compared to just enabling temperature reductions.
Opposite to your suspect the experiment shows the real life. On your roof and walls in summer gives the sun IR which will permeate more (in case of lightweight insulation) or less (in case of solid materials) the envelope, in winter the heated walls, floor and ceiling (about 99% of the heat energy will be stored there, only ~0,7 % in the rooms air). You're correct, most energy losses will be by heated air leaking outside the room and in summer by cooling off the lightweighters and glassed buildings. I know the 'american' way of construction very well and I am conscious of the problems there. Also in Germany these 'modern' means are more and more common, following McDonald as I suppose ;-)
To get rid with too much thermal losses we install very simple IR heating systems which will comfort the houses behaviour by spending most energy in the heating of the heavy and heat storeing envelope than into the light and volatible air. Result: The inner surfaces of the envelope will by radiation be constantly warmer than the air, no condensation can occur, never mold attack. And less lose of heating energy, by the way.
Besides no air convection, no dusty air in your sensible lung system, no asthma, no allergies - all done by IR heating and good airing by abolishing the airtightness of the windows (f.e. by putting out the upper rubber).
The hypothesis of mechanically transports of heat by conduction is mostly wrong and a fake promoted by insulation industries - it is valid only by direct contact between f.e. your warm hand or heated air and a colder surface. Here a lightweight insulation will take off less energy than a steel plate with same temperature. But the energy transports in materials are caused mostly by photones/phonones - in an electromagnetical way. Just in October there had been published a research result in CERN Grenoble. They cooled off a crystal to 5 K and then warmed it up from one end. Then they gave a mangetical field around the crystal and could change/move the energy transport rectangular. What will show that energy flux in materials is done nearly comletely by electromagnetic transports.
You can understand the senseless lightweight insulation also by a scientific research in practise: Appartment-House Nr. 6 was additionally insulated for a million 1988 and you can see the result for the heating costs - Nothing!
