Lstiburek Perfect Roof

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.

Lstiburek perfect roof.

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. Personally i don t view it as inverted. Joseph lstiburek talks about the not so controversial ways to maximize the efficiency and airflow of your roof and attic. 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.

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. Houses didn t used to rot but too many of them do now. Joe lstiburek talks about enclosure design principles for energy efficient houses. The perfect wall roof and slab building science podcast dr.

I ve been thinking about this concept for years but i m finally building a perfect wall house. There is no potential for condensation until interior moisture levels exceed 45 rh at 70 f during the coldest month. The physics doesn t change with floors or roofs so to get the perfect roof just pitch the wall same for the slab. But stay tuned for the perfect wall austin blog posts next week.

If all of the insulation is on the top of the roof sheathing this is pretty much a no brainer. Two layers are preferable to one layer due to increase in air flow resistance. Insulation air conditioning heating and forced air delivery systems have all changed the physics of how houses work. Here s a wall diagram to whet your appetite.

Lstiburek s commitment to advancing the building industry has had a lasting impact on building codes and practices throughout. Tilted it makes the perfect roof. The biggest benefit of the pmr is that the membrane is well protected. 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.

Simple physics complicated language. Layers of rigid insulation have staggered joints to facilitate airtightness. 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 is the founding principal of building science corporation.

Cost aside the most straightforward route is spraying closed cell polyurethane foam on to the underside of the roof deck.