We’re planning on building a new home this year and have begun discussions with 2 builders. We’ve encountered our first debate. One builder insists we should wrap our home in a Tyvec or similar product while the other insists on the black paper type product. Both argue its because their recommended product will let the new lumber in the home breathe and therefore not rot the wood. Can you please weigh in on this debate?
Building paper or Housewrap (Tyvec) is installed outside of the regular exterior wall sheathing on a home to provide an air barrier and help protect the exterior sheathing. This air barrier allows moisture that may be present in the wall cavities to escape to the exterior of the home while preventing air movement between inside and outside the home. For an air barrier to be effective, it must be continuous, without gaps or openings. Housewraps normally are available in wide sheets and are made of spun-bonded polyolefin or polypropylene. Building paper is constructed of regular paper that has been treated to increase moisture resistance and comes in long rolls of three-foot-wide sheets. Both these materials are good air barriers, but are not vapour barriers and will allow moisture to escape the walls of the new home.
These exterior air barriers are installed for two main reasons. The first reason is to prevent air movement through the wall of the home. These air barriers are normally installed on the exterior, because they also prevent wind from entering the wall cavity. If wind is allowed to blow into the wall cavity, we get what is known as “wind washing”, which can significantly reduce the effectiveness of insulation, especially fibreglass. Both of these materials will reduce the effects of wind, but may have other properties that may make one more desirable than the other.
The second major function of these exterior sheathings is to protect the wall cavity from moisture that may penetrate the siding. Most exterior siding materials have spaces or gaps to allow moisture to escape from the wall cavities that may enter from inside the home, or from outside, by wind-driven rain or other sources. The building paper or housewrap prevents this water from soaking the wall sheathing, and lessens the chance of moisture damage or rot.
Building paper has traditionally been used for this second function, and holds up very well over time and is quite effective. This is partially due to the normal installation method of overlapping successive sheets, with loose seams. This allows moisture to run down the surface, without getting behind the paper. This installation method may make building paper slightly better for this function than housewrap, but also prevents it from being a good air barrier. The loosely overlapped seams allow large gaps in the continuity of the sheathing, significantly reducing its effectiveness as an air barrier. If these overlapping joints are taped or sealed, as well as joints around windows and doors, building paper could be an effective air barrier. This is rarely done.
Housewraps normally are sold in sheets just under 3 metres wide, to minimize the gaps and joints in the air barrier. The joints are normally sealed with tape, as well as any wall penetrations and also around doors and windows. This minimizes the potential for errors in installation and increases the chances that the air barrier will be continuous. For this reason, Housewraps have become the norm, where building paper is much less frequently used on new homes. The only drawback to housewraps may be their moisture permeability. There is some question about the effectiveness of this material in protection of the wall sheathing from exterior moisture, over a long period of time. There is concern, as with any relatively new product, about durability and performance over many years.
This concern may be the reason that one builder is favouring traditional building paper over “Tyvec” for your new home. In my opinion, the effectiveness of either system is always a function of proper installation method. If either product is installed 100% correctly, they will both be equally effective. Chances are much greater that the Housewrap will be installed correctly, with no gaps or seams. Modern homebuilders should be knowledgeable about correct methods of installation of Housewrap, and information on proper techniques should be readily available from the manufacturers.
I am always cautious about widespread use of new products for major house systems, before long term testing has been done, but this may not be a concern here. Housewraps have been in use for quite a number of years, and there is no proof, that I know of, to backup the concerns over long-term performance. Only time will tell, but I would recommend the use of this over traditional building paper. Building paper has been effectively used as a covering for wall sheathing for decades, but this was mainly to prevent moisture damage to the sheathing, and wind washing.
Older homes were not built with today’s high level of insulation, vapour barriers and air sealing techniques and that has changed the material we use, significantly. What worked well in older, drafty homes may not be effective in modern house construction. I would ask both builders about specific installation techniques they use, and the reasons for their choice. Also inquire about their training and education, specifically modern building science courses, and weigh that along with experience. You may find that the builder suggesting the housewrap is better educated and may be better versed in modern building science.