NSC Advanced Slab Design

At North Star Construction, our designs are in a constant state of evolution. However, it is important to recognize that evolution is not radical change. It is slow and progressive change that, through testing, produces either a more efficient, healthier, and enduring entity or an entity that ceases to reproduce.

We scrutinize each aspect of our designs, our building processes, even our methods of accounting and invoicing to ensure a less costly and more efficient product with each year of evolution.

Our foundations and slabs have incorporated improvements from year to year without venturing away from the established elements of sound construction and design. We do not profess to have reinvented the wheel, but we have focused our experience and efforts on ensuring the finest, most efficient foundation available.

Our latest innovation, used on all North Star Construction projects, is the Advanced Slab Design (ASD). With this, we have developed the highest strength, highest insulation envelope, highest thermal mass, and the highest radiant heat tubing area of any of our designs to date. Our concrete strength has been increased 33 percent, our slab reinforcement is up 33 percent, our thermal mass is increased by a factor of 4, and our radiant tubing area has doubled. All of this is based on research that will help our homes attain the next level of efficiency and sustainability. We are offering the ASD not as an upgrade, but as a standard design element at no additional charge to our base contracts. We are providing these improvements to our standard designs in an effort to offset the rising costs of materials and energy in other sectors of the housing industry.

In discussions with our engineers and in private market searches, we have yet to find another company offering anything close to what we provide. However, we still remain well within the realm of low-cost housing. Our dedication to providing the best house at the best value continues to improve each year and the incorporation of the ASD is a critical element in what separates North Star Construction from the rest.

Structural Integrity
Our primary goal in foundation and slab design is structural integrity. Nothing supersedes our commitment to ensure that our homes have the finest design, engineering, materials, and craftsmanship to ensure a lifetime of structural reliability. Therefore, we have increased the strength of our concrete mix from 3/4 ­-- 3000 to 3/4 – 4000, thus increasing the strength of all concrete used in our structures by 33 percent (these numbers refer to the crushed stone size, 3/4 inch aggregate, plus the resistance of the cured concrete in pounds per square inch).

Reducing or Eliminating Slab Cracking
We have also turned our efforts to reducing a common problem which occurs in finished concrete slabs: cracking or surface fissures. As the use of under-slab insulation has increased, so has the propensity for slabs to experience an extreme number of surface fissures. In the same manner in which the desert floor produces chip-like “biscuits” of mud after a rain, concrete can experience the same effect although greatly diminished in visibility. This is called “curling.”

Our engineering team has determined that the vast majority of slab fissures are a result of different drying rates as experienced at differing levels within the slab. This is exacerbated by the introduction of a material – insulation or a vapor barrier – which can prevent moisture from being absorbed by the substrate. These materials cause the concrete to dry much quicker at the surface and much slower at the base, thus producing differential curing rates and the likelihood of surface fissures.

It is important to realize that all wet-poured, cement based materials cure by dehydration. As water is lost into the surrounding atmosphere, the mass of what remains decreases by the amount of water lost. If the mix has a high water content to begin with, it will have a high degree of water loss, leaving greater distances, although microscopic, between the remaining material mass. If the water content is low to begin with, then the mix will be stronger after curing but the pouring and finishing of the slab will be more difficult for the crew. Our intention is to increase the strength of the slab while providing a mix that can be placed in an efficient manner.

Sub-grade Insulation
Years ago, insulation under a concrete slab was unheard of. The compressive nature of insulation meant that it was not able to support such a load without compressing, thus losing all or most of its insulation properties.

Improvements in load-bearing capacities in rigid panel insulation have allowed the placement of insulation beneath slabs. However, most contractors install this insulation directly under the concrete or under 1 to 2 inches of sand. We have found that both of these methods do not allow for adequate dehydration of the lower half of the slab. In order to combat this, we pour our slabs on 8 inches of 3/4-inch crushed stone with a small amount of soil in the mix. Our insulation is placed beneath the stone/soil mix, and this in turn solves two problems:
1) It allows the slab to dehydrate into an area beneath the slab, equalizing the differential dehydration previously seen;
2) It allows us to increase the thermal mass of the insulated area without the added cost of increasing the concrete volume.

We use 2-inch rigid insulation beneath our slab and stone/soil mix coupled with a layer of Slab Shield, a closed-cell foam blanket with a central foil faced layer to provide increased insulation values. Our insulation is installed in an overlapping, diagonal layout on top of a fully compacted soil base. Footings and stem walls are also insulated with both 2-inch and 1-inch rigid panel insulation to greatly decrease sub-grade heat loss.

Solar Dedicated Radiant Tubing
In our ASD we have incorporated a secondary layer of radiant tubing that is dedicated to a closed loop, solar panel heating system. (In our base pricing, we include the radiant tubing for all sub-grade work at no additional cost. As an upgrade option on all our designs, we provide the installation of a full solar panel system which includes regulators, pump, valves, thermostats, wiring, and one panel for as little as $4950.

The radiant tubing dedicated to solar panel systems is broken into two sections:
1) A single zone of radiant tubing throughout the entire heated structure area for initial heating during producing days;
2) A secondary, external loop of tubing designed to provide solutions to two problems:
a. After the home has attained the desired temperature based upon thermostat settings, waste heat is routed to the area of the structure that will begin to draw heat as temperatures drop. This location is the sub-grade exterior of the home. By using waste heat to warm this area, later heat loss is decreased.
b. It provides an area for waste heat to be sent during times when heating the home is not needed. In spring, summer, and fall this excess heat can be dumped from the loop without heating the home itself.

The ASD is just one of many design evolutions we have developed and incorporated into our base models. We hope that you will take the time to review the other information listed on our home page.

Feel free to give us a call to discuss our designs and your new home!