Lstiburek Perfect Roof

Tilted it makes the perfect roof.

Lstiburek perfect roof.

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. Layers of rigid insulation have staggered joints to facilitate airtightness. 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. 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.

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. R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches. Here s a wall diagram to whet your appetite.

Houses didn t used to rot but too many of them do now. Insulation air conditioning heating and forced air delivery systems have all changed the physics of how houses work. I ve been thinking about this concept for years but i m finally building a perfect wall house. 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 s commitment to advancing the building industry has had a lasting impact on building codes and practices throughout. But stay tuned for the perfect wall austin blog posts next week. Simple physics complicated language. The perfect wall roof and slab building science podcast dr.

Joseph lstiburek is the founding principal of building science corporation. Joseph lstiburek talks about the not so controversial ways to maximize the efficiency and airflow of your roof and attic. Personally i don t view it as inverted. Cost aside the most straightforward route is spraying closed cell polyurethane foam on to the underside of the roof deck.

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. There s been so much stuff said about roofs that you sometimes lose perspective. That is one of the neat ideas of lstiburek s perfect wall.

There is no potential for condensation until interior moisture levels exceed 45 rh at 70 f during the coldest month.