Nail-laminated timber (NLT) is a large built-up member often used as interior structural members for floors, roofs, walls, and elevator/stair shafts. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change
(sometimes enough to fail fasteners), and even result in decay and loss of strength, construction moisture is an important consideration when building with NLT. This document aims to provide technical information to help architects, engineers, and builders assess the potential for wetting of NLT during building construction and identify appropriate actions to mitigate the risks.
Hemlock can have higher moisture content than most other native trees, causing them to sink. Hemlock lumens have large pits (valves) that allow easy transport of water into the wood.
Bigger rings = bigger lumens. Younger hemlock or hemlock tops are more susceptible to sinking. The bigger the rings the more likely to take on water.
The findings of recent studies from both eastern and western Canada have shown that the drying behaviour of subalpine fir (A. lasiocarpa) and balsam fir (A. balsamea) is similar, which allows common solutions to be applied based on research conducted on one species of fir or the other. This article summarizes previous research findings and good practices that can be adopted in the short term to improve the drying of fir.
Des travaux récents tant dans l’est que dans l’ouest du Canada ont montré que le comportement au séchage du sapin subalpin (A. lasiocarpa) et du sapin baumier (A. balsamea) est similaire, ce qui permet une application de solutions communes à partir de travaux effectués sur l’une ou l’autre variété de sapin. Le présent
document se veut une revue sommaire de résultats de travaux antérieurs et de bonnes pratiques pouvant être adoptées à court terme pour améliorer le séchage de cette essence.
In the pulp and paper and biofuel industries, real-time online characterization of biomass gross calorific value (GCV) is of critical importance to determine its quality and price and for process optimization. Near-infrared (NIR) spectroscopy is a relatively low-cost technology that could potentially be used for such an application. However, the NIR spectra are also influenced by biomass temperature (T°) and moisture content (MC). In this paper, external parameter orthogonalization (EPO) is employed to remove simultaneously the influence of T° and MC on the spectra before predicting GCV. EPO is of particular interest when one desires to transfer information from one modeling experiment to another, such as when developing a calibration model for a new property from the same material, or when it would be more efficient to divide the experimental effort. EPO was found to be an effective method for desensitizing a PLS calibration model to the influence of T° and MC, enabling robust and accurate prediction biomass GCV. Partial least squares (PLS) regression models developed with EPO always provided equal or better performance than models developed without EPO. The paper shows that experimental efforts and costs can be reduced by approximately one half while maintaining prediction accuracy and model robustness.
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This study was conducted with the aim of assessing the effects of log storage time and conditions at a BC mill yard on veneer production under mill production conditions. The second objective was to validate the FPInnovations LogdryTM drying model for developed for wood piles in Eastern Canadian mills. The software was used to generate drying rate predictions under the BC mill’s prevailing weather conditions and storage times for comparison with some measured residual moisture contents of Douglas fir logs kept in storage at the mill for six and nine months, sampled and peeled in a laboratory trial in 2016.
The 2016 lab trials suggested little effect of lengthy (winter) storage up to 9 months but mill experience suggests this is excessively long and logs deteriorate in terms of veneer production and quality considerably earlier. Unfortunately due to experimental circumstances the mill peeling trials for the 9 month stored logs were unable to provide an accurate assessment of the true effect on production. Mills trials indicated % heavy sap had remained fairly stable largely within the mill target of 14% to 17% over the storage periods. During the mill trials there were unavoidable heavy confounding effects of different average diameter for log groups and peeler knife condition affecting the expected veneer production variables.
The trials also demonstrated how pile size and height play a major role in protecting logs from drying; with very dry logs having a deleterious effect on veneer production. Logs held in small piles for 12 months or more, even with artificial ‘drying retardants’ such as end sealant and tarping were too dry for reliable peeling, causing very rapid knife wear, spinouts, veneer break-up and line blockages and significant lost recovery. The % heavy sap offtakes from these trials were just 2% to 4%.
LogDryTM provides a fairly good estimate of likely drying rate trends of mid-sized (35 cm/14” to 41 cm/16” range) Douglas fir under the BC mills historic weather conditions over 6 and 9 months.
LogDryTM (Birch setting) was closest to measured log MC in large diameter (46 cm/18”) logs but the Aspen setting was closer to measured MC in small logs (<30 cm/12”). In the limited sample of logs available from the mill in 2016 the 12” logs were much drier after 9 months storage than the model predicted, even on the Aspen setting. Further sampling of piled logs in the small diameter range is needed to verify this observation.
LogDryTM was used to estimate drying rates of logs stored before or after Summer. Modelling indicated a shorter viable storage window for logs delivered before Summer compared to just before Winter, especially in the 6-month range. Residual log MCs were very similar after 12 months regardless of start time.
Further work is required to better calibrate LogdryTM for major Western Canadian species, particularly Douglas fir, Spruce and Lodgepole pine, and reduce the calculation time for simulations. Further adjustment may be needed for simulating real drying rates in very small logs. The model assumption of similar residual MC after 12 months regardless of start time also needs to be verified.
Based on the data from this study and a literature review, there are two distinct trajectories for hemlock wood moisture content, depending on if the tree was felled before or after May. Hemlock trees felled before May gain the full benefit of spring drying according to the ambient conditions of their local micro-climate. Trees felled after May suffer from a physiological spike in moisture content that the tree generates to promote its growth and survive the summer soil drought.
The idea that a wicking treatment – leaving tops, branches, and needles attached to the stem after felling – would reduce stem moisture content and lead to reduced loss of western hemlock logs from sinking during watering was tested. This study did not show that wicking produces a different result from normal bucking in average stem moisture content if both groups are treated equally. Further, after curing for two months logs did not increase in moisture content during watering.
This report documents the instrumentation installed for monitoring moisture, indoor air quality and differential movement performance in a six-storey building located in the City of Vancouver. The building has five storeys of wood-frame construction above a concrete podium, providing 85 rental units for residential and commercial use. It was designed and built to meet the Passive House standard and, once certified, will be the largest building in Canada that meets this rigorous energy standard. Although the design and construction focused on integrating a number of innovative measures to improve energy efficiency, much effort was also made to reduce construction costs. One example of the design measures is the use of a highly insulating exterior wall assembly that integrates rigid insulation between two rows of wall studs as interior air and vapour barriers.
This monitoring study aims to generate data on long-term performance as part of FPInnovations’ effort to assist the building sector in developing durable and energy efficient wood-based buildings, which is expected to translate into reduced energy consumption and carbon emissions from the built environment. The monitoring focuses on measuring moisture performance of the building envelope (i.e., exterior walls, roof, and sill plates); indoor environmental quality including temperature, humidity, and CO2; and vertical differential movement between exterior walls and interior walls below roof/roof decks. In total, 79 instruments were installed during the construction.
The next steps of this study will focus on collecting and analysing data from the sensors installed, and assessing performance related to the building envelope and vertical differential movement. FPInnovations will also collaborate with CanmetENERGY of Natural Resources Canada to monitor heat recovery ventilators and to assess whole-building energy efficiency and occupant comfort. This is expected to start after the mechanical systems are fully commissioned during occupancy. Results of these upcoming phases of work will be published in future reports.
A total of 48 peeler blocks and 256 mini-billets were sampled from mills to investigate the effects of yard storage time, and artificial yard drying and sprinkling on residual moisture contents (MCs) and veneer quality. MC in fresh and stored log inventories varied greatly across mills according to geographic location of their wood supply zones, bark damage and loss, and storage time and conditions. The main findings were as follows:
1. DF logs supplied by three BC mills from the Cariboo, Thompson Okanagan, or Kootenay regions were highly variable in wood MC.
2. Winter-cut DF logs with high sapwood MC stored had good bark retention and high moisture retention over 6 and 9 winter-spring months. No effects on veneer peeling roughness from longer-term winter storage up to 9 months.
3. Summer-cut logs had little or no residual bark, or the bark slipped off very easily during debarking. Exposed, bark-free summer-cut logs can dry and crack on edges and ends very quickly, within a few weeks.
4. A marked decline in veneer quality with piling time in Summer for spruce and DF, suggesting an optimum window of processing of such exposed logs of about two weeks. Veneer quality and recovery suffered markedly once the logs had fully air dried mainly because of edge splits creating natural fragmentation of the ribbon.
5. Mills receiving dry-zone logs with much lower MC have a very limited storage window, especially over winter. As little as 2-3 weeks if bark is damaged or missing.
6. Veneer quality could not be definitively tied to log residual MC. Under the controlled laboratory conditions used here it was observed that peeling quality could still be good at low sapwood MC (35-40%) and or very high (MC>100%). Whether this is still the case in mill production is unknown.
7. Logs must never be allowed to fall below FSP and develop edge-checks or deep end checks.
8. Wax emulsion end sealants were effective at hampering drying and end checking on high MC logs, but not effective on low MC logs.
9. Sprinkling retained log freshness and peel quality in high MC DF for several months and prevented log drying and end splitting as well as inner log staining. Ends absorbed considerable extra moisture. Some variability in peel quality was noted.
10. The prototype EM1000 Ground Penetrating Radar could only be reliably used in log edge mode in DF. The unit would also require re-calibration for the very high sapwood MC in spruce and wet-zone DF logs.