Replies

1. 
   Guest_ | Mar 18, 2000 11:16pm | #1

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   Well you're right, it's not easy. Some treat the lower section of the gambrel roof as a wall and concentrate more on the upper section. With trusses, you wouldn't have a plate there to block airflow, although if the pitch of the bottom section is typically steep, you won't get much airflow from soffit type vents either.

   Is the ceiling of the 2nd floor flat? Or does it follow the contour of the trusses? Maybe you could treat it more like a regular attic.

1. 
   Guest_ | Mar 19, 2000 04:28am | #2

   *Gambrels were my first love ... our house is a gambrel..i've never had a problem venting them..we use a continuous soffit vent, our preference is a vented vinyl soffit...baffles tothe pitch break point, and baffles to a safe point above the insulation so the air can continue to move up to the ridge vent..the only brand of ridge vent we use is Shingle Vent II...the space at the eave above the soffit vent is typically behind the kneewall, the lower roof rafters (or trusses) sit on a purlin or plate atop the kneewall...the upper roof rafters (or trusses) also sit on the purlin or plate...the birdsmouth or heel forms a standoff distance at the purlin or plate allowing air to move past the p/p from the lower roof to the upper roof...if you want a simple diagram of this , email me and send me your fax number..Mike

1. 
   Guest_ | Mar 23, 2000 05:39am | #3

   *Foam it! This is one solution. If you use sprayed on urethane foam you do not need to vent. The foam is about R7 per inch so if you put in 6 inches you have R42. One of the reasons you don't need to vent is there is no air infiltration or moisture due to the foam. Also since the foam sticks to everything it comes in contact with, there are not voids for moisture to accumulate. It's not cheap but it's great stuff, no pun intended. Great stuff is about a 0.2 lb foam. The stuff the pro's use comes in 55gal drums and is about 2 lb foam. Tim

1. 
   Guest_ | Mar 23, 2000 03:40pm | #5

   *I recently framed a small storage building up with gambrel trusses. Whatever you do, do not use batts to insulate. Trusses in general don't insulate well with batts. This is due to the bottom chord of the truss being only a 2x4.The gambrel trusses we used were shipped in two halves and were assembled on site with double collar ties they provided. It is these ties that will create all kinds of difficult to insulate spaces.If it were my barn, and as I am doing with my own barn, I wouldn't bother venting it. Use the PUR foam or dense pack cellulose.The gambrel trusses make a nearly ideal situation for blowing cels in. Leave the drywall off the top collar ties, and dw the whole roof to that point. Blow in cels by snaking the hose all the way down both roof planes. Then dw the collar ties and pack out the remaining area by sliding the hose in from the gambrel ends.for ref. a 2-3 inch "skim coat" of PUR will cost $3.50-$4.00. It will give you R-21. Then use cels for the rest. The PUR can be applied such that it bridges the spaces in the trusses and makes compartments for the cels to pack in.To be honest - I am not sure if I would use the PUR in a new build. Atlas roofing products makes a nail base insulation that comes in various thicknesses. It can be applied over the trusses and sheathing. It eliminates thermal bridging, and still leaves plenty of space for blowing in cells between the trusses.For info on the Atlas NBI - http://www.arcat.com/details/atlas/prod0050.cfm?id=807sorry I can't make the link hot - just copy and paste itBecause the NBI comes in thicknesses up to 6" you could never insulate between the trusses, still have an R42 roof, and have plenty of places to hang stuff from.BTW - the top chord of the gambrel trusses was a 2x6Also - you may want to consider adding a small gambrel dormer on the side of this new roof. We just did this to our barn. The dormer is only 13 feet wide, but it bought us about 80 usable sf, and two giant double hung windows.-Rob

2. 
   Jeff_Anderton | Mar 23, 2000 03:40pm | #4

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   I would appreciate any comments or suggestions regarding the best method of venting a gambrel roof. I plan on building a traditional style barn this summer that will house a shop on the ground floor with office/ storage tucked into the second floor (within the gambrel roof). I hope to be able to use prefab gambrel trusses for the roof as opposed to custom framing, however the use of trusses leaves me wondering how in the world a roof of this type is vented. I live in a cold, western state at an elevation of nearly 6,000 ft. We commonly over frame our roofs here with a sleeper system that creats a cold roof with Boston ridge vents to afford ice dams and provide very adequate venting for temp. extremes. I hope to avoid a over frame of a gambrel roof. In fact I don't believe it could be be effectively accomplished. Any comments will be appreciated. A search of back issues has been of no assistance. Thanks

3. 
   MichaelAndrew | Jan 20, 2024 02:08pm | #6

   wow 2000.. 24 years later I'm looking for similar answers.. I have a gambrel that has upper attic vented by gable vent on each end and ridge vent.. the side attic area does have a 1.5" gap at top plate allowing air to upper attic.. I have a 8" soffit board that was not vented but was not sealed properly so must be sucking air through seems as I can see light. this could be vented

   I am looking for best way to provide vent channels & insulation in areas where I am taking out 2x4 studs and pushing my wall closer to the side roof slope. was considering foam board on side roof sloped rafters to provide radiant, R value, and also create vent shoot/channel. this would lead up above the top plate where I would put vent baffles at the roof break/transition in the upper attic to ensure that insulation does not cut off the ventilation.

   then I need help in best insulation in the rest of the walls where they are vertical creating a knee wall/side attic area situation.. what type of insulation is best inside the 2x4 studs and then should I put something on the BACK side of the studs to protect the insulation from wind washing and add R value (foam board) or is this creating an issue?