Lstiburek Perfect Roof

Two layers are preferable to one layer due to increase in air flow resistance.

Lstiburek perfect roof.

There s been so much stuff said about roofs that you sometimes lose perspective. Joseph lstiburek talks about the not so controversial ways to maximize the efficiency and airflow of your roof and attic. Here s a wall diagram to whet your appetite. Houses didn t used to rot but too many of them do now.

R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches. Unvented roof here again the choice of what insulation to use and whether to install it over or under the roof deck depends on the condition of the present roof the depth of rafters the r value you must attain and cost. Lstiburek s commitment to advancing the building industry has had a lasting impact on building codes and practices throughout. All insulation above roof deck the big deal with unvented roof assemblies is to control condensation or moisture accumulation on the underside of the roof sheathing.

There is no potential for condensation until interior moisture levels exceed 45 rh at 70 f during the coldest month. The first control layer is for bulk water or liquid water redundant terms used to make a clear distinction between water and water vapor which is the third control. Lying down it makes the perfect slab. Cost aside the most straightforward route is spraying closed cell polyurethane foam on to the underside of the roof deck.

Personally i don t view it as inverted. If all of the insulation is on the top of the roof sheathing this is pretty much a no brainer. One of the great features of these systems is that the water control layer is also the assembly air control layer and vapor control layer a k a the perfect roof see bsi 001. Layers of rigid insulation have staggered joints to facilitate airtightness.

The perfect wall roof and slab building science podcast dr. The biggest benefit of the pmr is that the membrane is well protected. But stay tuned for the perfect wall austin blog posts next week. The physics doesn t change with floors or roofs so to get the perfect roof just pitch the wall same for the slab.

Joe lstiburek talks about enclosure design principles for energy efficient houses. Insulation air conditioning heating and forced air delivery systems have all changed the physics of how houses work. The perfect roof the perfect roof is sometime referred to as an inverted roof since the rainwater control layer is under the insulation and ballast i e. I ve been thinking about this concept for years but i m finally building a perfect wall house.

Simple physics complicated language.