Lstiburek Perfect Roof

Houses didn t used to rot but too many of them do now.

Lstiburek perfect roof.

There is no potential for condensation until interior moisture levels exceed 45 rh at 70 f during the coldest month. 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. 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. R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches.

Joseph lstiburek talks about the not so controversial ways to maximize the efficiency and airflow of your roof and attic. Lying down it makes the perfect slab. 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. 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.

The physics doesn t change with floors or roofs so to get the perfect roof just pitch the wall same for the slab. Two layers are preferable to one layer due to increase in air flow resistance. The biggest benefit of the pmr is that the membrane is well protected. Personally i don t view it as inverted.

Lstiburek s commitment to advancing the building industry has had a lasting impact on building codes and practices throughout. The perfect wall roof and slab building science podcast dr. Joseph lstiburek is the founding principal of building science corporation. That is one of the neat ideas of lstiburek s perfect wall.

But stay tuned for the perfect wall austin blog posts next week. Cost aside the most straightforward route is spraying closed cell polyurethane foam on to the underside of the roof deck. I ve been thinking about this concept for years but i m finally building a perfect wall house. 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.

There s been so much stuff said about roofs that you sometimes lose perspective. Layers of rigid insulation have staggered joints to facilitate airtightness. Insulation air conditioning heating and forced air delivery systems have all changed the physics of how houses work. If all of the insulation is on the top of the roof sheathing this is pretty much a no brainer.

Here s a wall diagram to whet your appetite.