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Standards Specs and Upgrades

Modular Home Walls

Modular homes have have load bearing and non load bearing walls. The exterior walls and the marriage walls of the modules are load bearing. The interior walls rarely load bearing walls. Most modular home companies use 2x6 studs to contain R-21 insulation required in northern heating climates. In some southern cooling climates 2x4 might be used to keep pricing low.

Standard Exterior Wall Specs

• Studs - 2x6s spaced 24" on center
• Exterior Sheeting - 7/16 OSB glued and nailed or stapled to studs
• Insulation - R-19 fiberglass batts
• Drywall - 1/2" gypsum board, three layers of mud and two coats of primer paint
• House Wrap - Installed at the factory

Exterior Wall Upgrades

Studs - Some modular home factories have changed their specs to 16 inches on center to be comparable to old fashioned stick builders using the traditional spacing of 16" on center required with 2x4 studs. In my opinion 24" on center has two advantages. The price for twenty four inch framing keeps the modular home price lower and there is less thermal bridging in the exterior walls . The more insulation and less studs make the home more energy efficient and comfortable.

Exterior Sheathing - You have the option to upgrade to plywood on the exterior walls. I would not recommend this upgrade because it will raise the price of the modules and provide little to no benefit to the home.

Insulation - You have a couple of insulation upgrades for the exterior wall insulation.

• Spray Foam Insulation - Two inches of closed cell spray foam sprayed to the back side of the drywall. Spray foam provides increases the exterior walls to an R-24. In addition to being more energy efficient, the home will be quieter using foam in place of strictly fiberglass batt insulation. The spray foam will stiffen the exterior walls minimizing wall cracks due to transportation and setting the home. The disadvantage to using foam is the high cost. Depending on the manufacture, two inches of spray foam starts around $20 to $40 per lineal foot of the exterior walls.
• Rigid Insulation Board - To achieve an R-31 on the exterior walls of your modular home you could opt for two inches of rigid insulation board to be installed to exterior of the exterior sheeting. The cost to use rigid insulation board will drive the price of the modular home up because all windows and doors will require being padded out. Rigid insulation board will not allow you to install some onsite optional upgrades to the suggested manufactured installation directions.
• Drywall - 1/2 inch thick drywall is more than adequate for the interior wall covering. If you have an attached garage, 5/8 fire rated drywall will be required in most states to meet fire codes.

Marriage Walls

The marriage wall is the wall between the modules of a prefab house. In a double wide modular home there's only one marriage wall. The marriage wall is a load bearing wall that is located inside conditioned space and does not require insulation. Since marriage walls do not require insulation they can be constructed using 2x3 and 2x4 studs at 16 inches on center

Marriage Wall Specs

• Studs
  • Ranch Homes - 2x3s framed 16 inches on center
  • Cape Cod and Two Story Homes - 2x4s framed 16 inches on center
• Exterior Sheeting - Nothing
• Insulation - None
• Drywall - 1/2" gypsum board, three layers of mud and two coats of primer paint

Marriage Wall Upgrades

Studs - I personally do not see any need to upgrade the studs on the marriage walls. Some manufactures use 2x4s on ranch homes. I prefer to see 2x3s to keep the depth of marriage wall to six inches thick rather than eight inches thick when 2x4s are used.

Sheathing - adding sheathing of some sort to the marriage wall will make the modules stiffer. The stiffer the module, the less drywall cracking will occur due to transportation and set. The minimum sheathing for a marriage wall is structural board which is a rated dense cardboard. Often 7/16 OSG can be used to cover the marriage walls at close to the same price.

Interior Walls

Interior walls in a modular home are rarely load bearing and therefore can be constructed with 2x4 studs. Insulation is not installed in these walls as a standard, but can be upgraded with insulation to minimize sound transmission within the house.

Interior Wall Specs

• Studs - 2x4s framed 24" on center
• Ceiling Height - 8' Tall
• Drywall - 1/2" gypsum board, three layers of mud and two coats of primer paint

Interior Wall Upgrades

Back Bracing - If you are planning on having a wall in your home contain a number of pictures or hanging items, having additional bracing installed will insure your wall hanging items are secure. To back brace these walls, the factory will dato out 7/16 of space and install oriented strand board in the recess. If you opt for this modular home upgrade, you will never need to hunt for studs on that wall.

Ceiling Height - Increasing the ceilings to have the maximum height of eight feet six inches to nine feet tall is highly recommended. Taller ceilings in small modular home will add a bigger feel to a home with limited square footage at a nominal price. In addition, you will never be able to make this upgrade once the home is built.

Interior Wall Insulation

Adding insulation to your interior walls will minimize sound transmission. Adding interior wall insulation during module construction is nominal, typically less than two hundred dollars a room. Insulating interior walls is not necessary by code, but the following spaces will benefit from being insulated:

• Master Suites - If your master bedroom is adjacent to living spaces, bedrooms or common rooms in the home adding insulation to the walls will keep sound out and from entering your bedroom.
• Libraries and Home Offices - Places where you will be working will benefit from having insulated interior walls. This is especially true if you are telecommuting and you have children. A home office in a modular home needs to be a quiet space.
• Bathrooms - Insulating the interior walls of all bathrooms will minimize ugly bathroom sounds from entering living spaces in your home. In addition if you have a shower singer who sings off key, you can save the family from torture.
• Family Rooms - Insulating your modular home's family room walls will keep peace through out the home. Often the family room and the formal living room is divided by the marriage walls in the center of the home. Adding insulation to the family room will allow for children to be children even if they are big kids who own the house.