How long does it take a slab to dry out before flooring can be installed?

This is a very important question. Moisture is a problem with fresh concrete slabs, and if you install your floor in a wet slab you will have a lot of problems in the future.

Basement Finished Superior Wall1
Concrete slab in the basement after finishing. We are now around 2 months after the installation. The concrete walls are already insulated (we used Superior Wall pre-cast foundations in this project)

Variables that affects the concrete moisture include:ambient relative humidity, concrete permeability, amount of water in the concrete when it is placed, slab thickness, presence (and thickness) of a vapor barrier in contact with the slab bottom, and method used to finish the surface.

Here you have the needs depending on the type of floor to be installed:

  1. Impermeable flooring (Vynil, for example): Internal relative humidity around 85% or surface moisture–vapor emission rates (MVER) of 3-5 pounds of moisture per square-feet over 24 hours
  2. Wood floors: 75% internal relative humidity and an MVER of 3 pounds of moisture per square-feet over 24 hours (National Wood Flooring Association recommendation)

In practical terms, just remember that to achieve the recommendations it takes time. In normal average conditions (relative humidity around 50% most of the time and temperature above 65F, concrete water-cement ratio of 50%) a 4-inch slab can take up to 3 months to dry before you can apply a floor there. But remember that this 3 month period starts only when the cement is dry.

You have some specific tests for that, that are too technical to describe here. Just to mention, the calcium-chloride test and the internal relative humidity test are tow that can be applied for this evaluation.

One of the most important features is the vapor barrier/vapor retarder. Without a vapor barrier the slab will never dry out. That’s why the construction codes put the obligation to use a 6 mils vapor barrier there. The 10mils and also the 15 mils poly sheet can better control the moisture. The best location for the vapor barrier is in direct contact with the bottom of the slab.

If insulation is used over the concrete slab a 4-month drying time should be respected before installing the EPS (normally the EPS absorbs 0.5% by volume).

To have more detailed information about that you can click here and check the Concrete Construction magazine


Snow Loads on Roofs: take care of it

How much snow can a roof support? It depends on the way you design it.

Image result for roof with snow
Photo credit: click here

780 CMR Commercial Mass State Building Code Table 1604.11 provides snow load for roofs. The Ground Snow Load ranges from 45 lbs to 65 lbs per horizontal square foot depending on each community and the zone in which it is located. The Residential Code 5301.2(5) for 1 and 2 families’ ground snow ranges offer different values again depending on the community and zone of 25 lbs. to 50 lbs. per horizontal square foot. To determine the snow load for your specific community and zone refer to the chart.

A flat roof, gable roofs and roofs with multiple valleys and snow gathering points will vary the weight differential factors as will the number and type of roof coverings effect the value. First we have to presume that the structure has been constructed to sustain the minimum snow load requirements of the code.

The weight of snow/ice, not the depth, is critical in assessing a roof’s vulnerability. The water content of snow may range from 3% for very dry snow to 33% for wet, heavy snow to nearly 100% for ice. An inch of water depth weighs 5.2 psf. Thus, a roof designed to a carry a snow load of 20 lbs per horizontal square foot is expected to support nearly 12 inches of wet, heavy snow. If using the heaviest wet snow value for roof designed to sustain 40 psf of snow load then it can be viewed that it should be capable of supporting nearly 24″ inches of wet heavy snow. If the snow moisture content is less, the depth of snow for sustaining can be greater.

Please use this information as a tool to assist you . If you need more precise information please contact a structural engineer to measure your roof loads. Roof failures may not be solely attributed to built up snow, there may be other actions that occur that affect the roof structural stability and sustainability.


Deck railing: pay attention to the rules

timbertech-banner-deck railing Wise Home Building blog
TimberTech Radiace® railing system

Regulations and codes are a pain in the neck for builders. But they are necessary, and some of them are really important to make your house a safer place to live. Deck railing codes are really important, and remember them when building your deck (if you are not using a contractor)

All decks higher than 30″ above grade must have a guardrail. But if your deck is lower than 30″ and you would like to install a railing system you must still meet code requirements. The International Residential Code (IRC) for single family houses requires guardrails to be at lest 36″ in height measured from the deck surface to the top of the rail. You are allowed to build taller guardrails as long as they conform to all other requirements stated in the code (click here to check all code recommendation for deck construction).
Deck Cantilevers

cantilevered-deck-crop Wise Home Building blog
Image credit:

Instead of putting a girder at the end of the joists, you’ll need a beam under the joists, so they can extend past that support. This framing style is called post and beam, and the overhang is a cantilever. If you would like to have a a cantilever deck the code have the rules in Section R507.5. Deck joists can cantilever up to 1/4 of the joist span. But you’ll notice when you look at the portion of the span table for joists with cantilevers that the joist span for decks with a cantilever is often less than the span for the same sized joist without cantilevers. The next subsection requires that solid blocking is required over the beam when there is a cantilever.

Even if your local code jurisdiction hasn’t adopted the 2015 IRC, most building officials will look favorably on an ICC sanctioned code provision. So run the table by your building official for approval before using it. And stick with a builder or contractor that understand the rules and local codes, of course.