Firm Foundations for Log Cabins

Deciding on the type of foundation for your log cabin is one of the most important decisions you’ll make in the building process. Placing your log cabin on a solid foundation is critical to its long-term support and longevity. Knowing what foundation types are available as well as learning exactly what goes into building a log cabin foundation are critical to your success and satisfaction as a log cabin owner.

Building log cabin foundations is similar to constructing foundations for most other light structures. By “light,” that means residential or recreational buildings, which are the categories your log cabin falls into. That’s regardless if it’s a small, one bedroom get-away cabin or a two-story, three-bedroom full-time home. The design and building principles universally apply.

What varies are the individual factors around your personal log cabin project. These include the specific building site, the overall intended use, as well as the ever-present budget limitations. Sorting through these parameters is something every log cabin project owner faces. Like everything else in building, a little knowledge is helpful, but a lot of information can be invaluable.

Although Conestoga Log Cabins doesn’t provide foundations with our log cabin kits, we’ve sold over 3,000 log homes and are proud to have at least one in every state as well as in seven foreign countries. Each log cabin sits on a foundation, and, as such, we’ve learned a lot about foundations. Now we’d like to pass on the basics of what we know about building firm foundations for log cabins.

According to the International Association of Certified Home Inspectors (InterNACHI), the purpose of a foundation is to “transfer the load of a structure to the earth and resist loads imposed by the earth.” Many factors impact your foundation decision including climate, geography, water tables, topography, properties of the soil, local code requirements and personal preference. Budget is also a major influence affecting your choice.

Regardless of the type of foundation, the majority of American log cabin foundations are built with some form of concrete — either poured, block or precast. Some types of foundations used for log cabin homes are slab-on-grade, pier, crawl space and full basement. Each has their advantages and disadvantages. Let’s take a quick look at each type before going in depth on what makes for a good log cabin foundation.

Slab-On-Grade Foundations

A concrete “slab” refers to a thick, flat, horizontal mass of poured concrete that’s level across its top surface. Generally, the concrete slab is the same size as the outer dimensions of the log cabin and uniformly supports the cabin’s weight — including transferring concentrated loads from the top to the bottom where it’s dispersed to the supporting earth.

Think of a concrete slab-on-grade foundation the same as a basement floor being raised to the surface and acting as the main floor of your log cabin as well as its outside perimeter foundation walls. A slab-on-grade foundation is an all-in-one process that incorporates independent conventional foundation components of footings, walls and a floor.

Slab-on-grade foundations are best suited to smaller and lighter structures that are situated on flat lots where surface and ground water drainage won’t present problems. They’re also the least expensive to build. They require minimal excavation and materials and are quick to construct, thereby saving labor costs.

Let’s review some advantages and disadvantages of using a concrete slab for your log cabin foundation.

Advantages of Concrete Slabs

• Requires less labor and excavation, which means quicker completion and lower cost
• Prevents rodents from nesting under your log cabin
• Provides accessible entrances with only a step or two, which can be important if occupants have difficulty climbing stairs.

Disadvantages of Concrete Slabs

• Limits access to any systems installed under floors such as plumbing, heating and electrical.
• Leads to uneven flooring, drainage problems and moisture penetrating through cracks when poorly constructed
• Creates unpredictable performance in areas of prolonged frost

Pier Foundations

Builders commonly use piers for log cabin foundations. They consist of concrete cylinders or “piers” that are cast in place and deliver the cabin’s weight from its framing members down through the earth to footings placed on solid bearing ground. That might be natural earth that’s undisturbed by excavation, bedrock or it could be artificially-placed granular fill sufficiently compacted to support weight and prevent settling.

Concrete piers elevate above ground and allow air movement under your cabins lower wooden structure of beams and floor joists. There is no concrete floor or side walls to contend with, and normally there’s no system of drainage pipes or ground water control. Piers are placed at strategic points where framing loads are heaviest, such as the ends and middle of beams or where load points from roofs concentrate.

Builders use piers foundations where the ground is uneven. The lower surface where piers contact solid ground can be highly irregular as piers are all capped at the top at the same elevation. Piers are a simple solution to building your cabin on rough terrain and enjoying a flat, level floor.

Piers are also used in conjunction with other foundation types to support secondary and lighter component of a log cabin. Theses might be concrete piers and footing pads for porch supports or to hold up a raised wooden deck. Piers are common for outbuildings as well.

These are a few advantages and disadvantages to using piers for log cabin foundations.

Advantages of Pier Foundations

  • Allows access to electrical and plumbing systems
  • No issues with termites
  • Saves money as it’s less expensive than a crawl space
  • Less insulation is required since there is no air under the building
  • Provides a suitable solution for sloped lots

Disadvantages of Pier Foundations

  • Provides easier access for rodents

Crawl Space Foundations

Crawl spaces are similar to pier foundations where they elevate your cabin’s wood floor structure above the ground, giving you enough room to crawl under it, but not enough height to stand up like you’d have in a full basement foundation. Crawl spaces are normally two to three feet in height, and the floors are covered by a concrete “skim coat.”

The main difference over a crawl space compared to piers is that crawl spaces have solid concrete perimeter walls. These walls are similar to a full basement where they absorb the outer wall weight from the cabin and transfer it to concrete footing on hard earth. The inner cabin weights from posts and beams are supported within the crawl space by interior curb walls, piers or sometimes adjustable metal teleposts.

Building a concrete crawl space for your log cabin can be the perfect compromise between a simple slab or a multiple pier foundation and where a full-height, in-ground basement is not required or can’t fit your budget. Many log cabin owners find crawl spaces highly useful. They’re perfect for storage as well as offering excellent weather protection and insulation.

Crawl spaces can be either heated or left unheated, provided your wood floor assembly is insulated. Access to a crawl space has numerous options. If there’s sufficient height, access can be through a doorway formed in an exterior concrete wall. Some crawl space accesses are made as trap-doors in the wood floor and located in out-of-the-way places like closets or mechanical rooms.

Consider these advantages and disadvantages to crawl spaces when deciding on your best log cabin foundation.

Advantages of Crawl Spaces

  • Accommodates HVAC and plumbing systems, making them accessible for maintenance
  • Adds curb appeal with a perimeter wall, which can be constructed out of material such as stone or brick
  • Offers greater affordability than a basement with less excavation, material and labor costs
  • Keeps our Rodents

Disadvantages of Crawl Spaces

  • Creates a potential problem where moisture buildup may possibly not be vented properly
  • Leads to unwanted materials (dust, moisture) circulating through your ventilation when ducts are poorly installed or unsealed
  • Makes for tricky maneuvering when servicing mechanical systems or storing items

Full Basement Foundations

Complete or full in-ground basements are commonly used when excavation requires that your cabin’s concrete footings have to be placed below the frost line. Then concrete perimeter walls need to be constructed with sufficient height, so your cabin’s wood floor structure is above contact with the natural ground.

In cold climates like the Northeast, many areas have building code requirements where footings have to be placed four to six feet below the ground line to prevent frost penetration that can freeze the footing base and cause it to swell or buckle. In this case, it’s economical to dig a bit deeper or build the basement walls higher above the surface so a full basement can be used as a conventional living or utility space. Normally, full basement wall heights are eight feet.

Deciding on whether to build a full in-ground basement under your log cabin depends mainly on the site specifics. That includes frost regulations, site conditions such as ease of earth excavation versus expensive preparation like rock blasting, as well as the intended use where you need additional square footage at a blended cost by using the basement as more than a mechanical and storage space. It also greatly depends on your funds.

These are some advantages and disadvantages of using a full basement under your log cabin.

Advantages of Basements

  • Provides additional storage space, workshop areas or recreational places
  • Offers an extra living space without increasing log cabin’s footprint
  • Could be used as a garage
  • Provides a cooler space during warm weather
  • Creates a location for mechanical equipment with easy access for maintenance and repairs

Disadvantages of Basements

  • Increases budget due to more expensive requirements with excavation, material and labor costs
  • Presents a potentially damp and dingy area unless properly sealed, insulated and heated
  • Limits options in areas with high water tables or unsettled soil
  • Creates a cave-like setting if there aren’t any windows added to allow daylight in

These are the four main foundation types to consider when planning and building your log cabin. Deciding on your foundation type is fundamental once you’ve chosen your floor plan. The strength and stability of your Conestoga log cabin rest with the foundation you build, and you only have one opportunity to build it right.

All Conestoga log cabin kits can be built on one of these four foundation types. Which one is right for you depends on a combination of these primary factors or “influences.”

Influences on Choosing Your Log Cabin Foundation

Your log cabin foundation transfers the load or weight from your cabin’s roof, walls, floor and occupants to solid ground where it’s safely disbursed to prevent sagging or failure of your wood frame assembly. Your choice of how to do this is influenced by:

  • Your site soil or ground conditions such as rock, clay, gravel, sand or organic earth
  • Your site’s drainage and standing water tables
  • Your local climate conditions, especially frost depth
  • The size of the log cabin you’ve selected
  • Ground contours around your building site
  • How much extra space you desire
  • The mechanical requirements of your cabin
  • Your log cabin building project budget

Budget is a huge factor in almost all log cabin projects. Generally, the larger and more complex you make your foundation, the more it’s going to cost. There are guidelines to foundation costs just like there are guidelines to log cabin kit costs. Feel free to contact a knowledgeable representative at Conestoga Log Cabins to discuss your specific site conditions and for advice on what type of foundation is best for you.

While Conestoga doesn’t become involved with the foundation segment of your project, our staff has considerable experience in all parts of the construction process and will be happy to help guide you in the right direction. With that, we’re supplying you with more helpful details about the steps involved in building the four types of log cabin foundations. Here is some basic information on excavation, soils, concrete, drainage, insulation and backfill.

Log Cabin Excavation and Soil Conditions

What lies under the site you’ve chosen for your log cabin will be the most important influence in what type of foundation is best. Soil conditions were placed there by nature, and it’s wise to work with the natural soil conditions rather than modifying them.

There are two natural forces working against your log cabin foundation:

  1. Subsidence

 This is where soil moves or slides away from your foundation over time. It can leave your foundation bare or, in worst cases, it can slide the foundation along with it. This can include your entire log cabin.

  1. Settlement 

This is a more common issue and occurs when a foundation was placed on unstable or improperly compacted soil that then consolidates or shrinks. Settlement can affect one part of a foundation, leaving your cabin lopsided, or it can occur across the entire foundation footprint.

Preventing subsidence and settlement occurs from understanding your native soil conditions and preparing the site to work with, not against them. The main soil conditions you’ll encounter will be:

  • Organic surface materials like topsoil and decomposing plant material. These have no structural stability and must be removed before building on. Organics can be used as top dressing in backfilling your foundation and blending it into the final landscape.
  • Granular mineral materials such as sand, gravel and loose stones. These are excellent surfaces and provide great water drainage. They also compact well for positive stability.
  • Clay-based mineral materials. Clay is common throughout most of the nation and is often found with a similar material called glacial till. They’re left over from ancient processes and are completely inert, or resistant to organic breakdown. Clay and till do have disadvantages, though. They have next to no drainage ability and are completely unstable once disturbed and wet.
  • Bedrock is the most stable foundation surface available. Foundations can be placed on rock without footing, as solid rock is far denser and weight-friendly than most concrete mixes. Rock’s disadvantage, however, is that it can be expensive to remove if necessary.
  • Imported structural fill. Often building sites are excavated, and the bottom surfaces are uneven. It’s common to import structurally-rated granular fill like crushed gravel and mechanically compact it in place for a solid, level base. A word of caution: Importing and compacting fill may require a geotechnical engineer’s approval to your building department.

Concrete for Your Log Cabin Foundation

Regardless if you choose a slab, pier, crawl space or full basement foundation, you’re going to pour concrete at some point. There are variations of Preserved Wood Foundations (PWF), but our recommendation is to avoid them in most circumstances and go with a timeless product. That’s concrete’s real value — it’s there forever.

Concrete is the best natural building material available. It begins in a plastic and malleable state that can be formed into nearly any shape and size. Once it’s cured, concrete has incredible structural strength and water-resistant abilities.

You’ll hear two terms that are often confused. “Concrete” is a mixture of air, water, paste and aggregates or granules. “Cement” is the powder that contributes to making the paste, and it’s usually referred to as “Portland Cement Powder.” Therefore, the correct terminology is a “concrete foundation,” not a “cement foundation.”

It’s also helpful to know that concrete doesn’t dry to harden. It undergoes a chemical reaction due to the precise blending of ingredients. This process is called “hydration” and is subject to many factors such as the ratio of air, water, powder and aggregates. Concrete curing is also highly susceptible to temperature. Should concrete freeze during the hydration period, it can later crumble and fail. Conversely, should concrete overly dry or dehydrate while curing, it can lose strength, then begin to flake, spall or entirely fail as well.

According to the Portland Cement Association, the correct mixture provides the best workability for fresh concrete and the necessary durability and strength required of the hardened concrete. Typically, a good concrete mix will contain:

  • 6 percent air
  • 11 percent Portland Cement Powder
  • 41 percent coarse aggregate like gravel or crushed stone
  • 26 percent fine aggregate, such as sand
  • 16 percent water at the desired optimum temperature

Concrete mixtures can reach a high degree of engineering science. Admixtures to be aware of are plasticizers for smoothing, mesh fibers for strength, color additives for aesthetics and varying ratios for strength.

Another important issue to know about concrete for foundations is that it comes ready-mixed from batch plants in different strengths. These are rated in their capability of supporting or withstanding pressures and loads rated in pounds per square inch or PSI. They’re also rated in MegaPascals (MPA) for some applications where the metric system is used. Standard strengths are:

  • 2,000 PSI or 20 MPA
  • 2,500 PSI or 25 MPA
  • 3,000 PSI or 30 MPA
  • 3,200 PSI or 32 MPA

Increasing concrete strength is achieved by altering the ratio of Portland cement powder in relation to the aggregate content. Water and air entrainment also need to be adjusted accordingly.

An important tip to leave you with regarding concrete pours — be extremely careful about adding extra water to concrete after it’s been properly mixed. This can completely alter the hydration process and cause your pour to fail. Adding water is a last resort only to be used if your concrete is setting too fast and has to be reduced to save it.

Drainage, Insulation and Backfill for Your Log Cabin Foundation

After you’ve built tour slab, pier, crawl space or basement concrete foundation on solid-bearing ground that can’t settle or subside, you still have important tasks to accomplish before it’s ready to accept your Conestoga Log Cabin kit. That’s providing adequate drainage, insulating it if necessary and placing free-draining backfill against the outer walls and under the slab.

In all but the driest climates, ground water is going to be an issue for at least part of the year. It’s part of the natural climate, but it’s easy to control as long as you pay attention to a few principles. Water needs to have free passage from its source to its destination. Make sure your foundation doesn’t act like a dam. Trapped water builds up and will find the path of least resistance inside your foundation — and that could be on your basement floor.

Ground water is also subject to a force called hydrostatic pressure, where water builds its pressure-volume and forces its way through cracks or fissures in concrete walls. The easiest way to prevent hydrostatic pressure is by providing free drainage around your foundation perimeter. Primarily, this is done with granular backfill like gravel, drain rock or crushed stone. It’s also accomplished with materials like dimple board that’s placed against your foundation wall and creates artificial channels for pressurized water to escape.

The simplest and most basic forms of water control in walled foundations are damp proofing, or “tarring,” the walls and installing perforated drain pipes around the perimeter to passively bleed water away to a pit or storm drain. Flexible piping is still used in some areas, but it’s worth the investment to install rigid, glue-together pipes that can withstand the pressures of backfill.

If you’re planning on heating your crawl space or in-ground full basement, consider using exterior rigid Styrofoam insulation on the exterior walls that extend down below the frost line. If your budget can handle it, there are various brands of insulated concrete forms or “ICFs” that incorporate the concrete walls being cast within rigid-foam cores. These are exceptional for energy efficiency and strength but require specialized knowledge, considerable reinforcement and an exact concrete mixture. Building ICF foundations is best left to a professional who’s experienced with this tricky technique.

Common Foundation Problems

Almost all foundation problems stem from improper construction practices when they were first built. You can easily prevent future issues by paying attention to these basics we’ve laid out. The most problem foundation issues are:

Excessive settling as a result of building on unstable ground. You can make corrections by lifting the foundation or slab jacking.

Concrete separation resulting from improper mixes, adding excess water or causing interruptions during the pour. Correction is made by filling the voids with a trowel-on mixture.

Water ingress caused by hydrostatic pressure or improper drainage. Correction is through relieving backfill pressure and installing porous material with perimeter drains that direct water away from the walls and footings.

Building a firm foundation for your Conestoga Log Cabin is critical to your project’s success and years of trouble-free enjoyment. Choosing the right type of foundation that best suits your needs is the start, and we’re here at Conestoga to help you with the process.

Contact Conestoga today to learn more about our durable, affordable and beautiful log cabin kits.

Sources

  1. https://www.nachi.org/
  2. http://www.cement.org/cement-concrete-basics
  3. https://conestogalogcabins.com/blog/firm-foundation/  
  4. http://www.logcabinhub.com/log-cabin-foundations/
  5. https://www.concretenetwork.com/concrete/foundations.htm
  6. http://www.cement.org/cement-concrete-basics/cement-and-concrete-basics-faqs