The sequence of construction steps is up for interpretation and may vary depending on your contractor or construction manager. Some builders swear by installing the vapor barrier first, while others claim that laying the vapor barrier over the insulation is better. Both may be correct.
On most projects where insulation meets the under-slab vapor barrier, we have found that the project teams elect to install their insulation first and to lay the vapor barrier over top. Various industry leaders have commented on the advantage of placing the vapor barrier directly beneath the slab.
When using this approach, it is important to ensure that the vapour barrier is installed correctly. The vapour barrier should be installed on the warm side of the insulation to prevent moisture from penetrating the insulation and potentially causing damage or reducing the insulation's effectiveness.
Location: Floor underlayment is positioned between the subfloor and finished flooring, whereas floor vapor barriers are typically installed beneath the underlayment or directly on top of the subfloor, depending on the specific requirements of the flooring system.
The common taboo against a double vapor barrier arises from a very real concern: If you have a Class I vapor retarder (less than 0.1 perm) on both sides of a wall, that wall has virtually no drying potential in either direction.
This is because an air gap provides an additional layer of insulation that helps to prevent heat from passing through the barrier and into the living space. If you are installing a radiant barrier, it's recommended to leave an air gap of at least 25mm (1 inch) between the barrier and the surface it's installed on.
In Most Cases, Attic Insulation Does Not Need To Provide A Vapor Barrier.
Lastly, the geographic location of the construction needs to be taken into careful consideration when deciding the proper placement of a vapor barrier in relation to the wall assembly. Properly placed vapor barriers should be installed on the warm, humid side of a wall.
A vapor retarder that is torn or punctured provides a pathway for moisture to enter the slab from below. The American Concrete Institute's Guide for Concrete Floor and Slab Construction recommends that the thickness of the vapor retarder be at least 10 mils.
Yes. Hardwood flooring is quite sensitive to moisture and it's always worth adding a moisture barrier during installation. It is a necessity with concrete subfloors and damp areas, but water-resistive underlayments should be considered with other subfloors as well.
Because a vapor barrier is a low permeable barrier, it keeps moisture from passing through. This is beneficial to keep moisture away from a dry surface but will trap moisture behind it if installed on a water-damaged concrete wall, causing the wall to fail further.
If installed on top of attic floor insulation, the foil will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation.
Vapour control layer building regulations
12 require that all new builds have an approved VCL fixed to the warm side of all insulation and cover the external framed wall area. It must be fitted at 250mm centres to the top and bottom of frames, around openings, at laps and wherever there has been any damage.
Overlap seams of the vapor barrier a minimum of six inches and tape down the seams with the manufacturer's engineered seaming tape or approved method. Make sure the vapor barrier is free of any dirt, debris, moisture, or frost when applying the tape. A dry rag or towel works well to wipe it clean.
Kraft-faced insulation includes a paper vapor retarder, which helps prevent mold and mildew. Kraft-faced insulation should be installed in exterior walls, exterior basement walls, and attic ceilings by pressing the product into the wall cavity with the paper side facing outward, towards the installer.
General rule of thumb is that the WATER barrier goes on the exterior wall, just under the outer cladding, and the VAPOR barrier goes on the warmest side of the wall, up against the sheathing. You can have only one water barrier, and only one vapor barrier, so you would need to remove the existing one.
In the 2021 edition of the International Residential Code (IRC), the guidelines were revised to recommend a minimum 10 mil vapor barrier for use under concrete slabs in residential buildings instead of a 6 mil.
15-mil vapor barriers are slightly thicker and more durable than 6-mil, 10-mil, and 12-mil liners.
Roll out Vapor Barrier membrane into desired location. Be sure to stagger end laps and overlap side laps by a minimum of 3” as indicated on the surface film of the products. End laps should have a minimum of 6” of overlap and end lap "T" joints should be cut at a 45° angle.
The sequence of construction steps is up for interpretation and may vary depending on your contractor or construction manager. Some builders swear by installing the vapor barrier first, while others claim that laying the vapor barrier over the insulation is better. Both may be correct.
For crawl space projecs that require a vapor barrier installed within walls, builders commonly use a thinner plastic sheeting option such as 6 mil, but for the best durability in the crawl space, our vapor barrier experts instead recommend choosing 8 mil plastic sheeting.
From a moisture-protection standpoint, it is my strong belief – reinforced by decades of ACI study and expert opinions – that the under-slab vapor barrier should be located directly below the slab, without the use of a layer of granular fill (sometimes sand) sandwiched between the slab and vapor barrier, often referred ...
“For minor projects, the absence of a vapor barrier leads to water intrusion, leading to an unstable foundation or a cracked slab.” The American Society for Testing and Materials (ASTM) outlines national standards for underslab vapor barriers.
Is DuPont™ Tyvek® a vapor barrier? No, DuPont™ Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.
If you do not like the sensation of dirt or dust on your skin, you will want to wear gloves and cover exposed skin. The dust of cellulose can still be hazardous for your eyes and lungs. If you are near cellulose being installed and do not wear a mask, you will inhale dust and irritate your lungs.